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This article, titled "Retracted: Analysis of Characteristics of Tennis Singles Matches Based on 5G and Data Mining Technology," has been retracted by the publisher, Hindawi, due to evidence of systematic manipulation of the publication and peer-review process. The publisher cannot vouch for the reliability or integrity of the article. Wiley and Hindawi have implemented additional measures to safeguard research integrity. The corresponding author has been given the opportunity to respond to the retraction. [Extracted from the article]

This article has been retracted by Hindawi following an investigation undertaken by the publisher [[1]]. We wish to credit our own Research Integrity and Research Publishing teams and anonymous and named external researchers and research integrity experts for contributing to this investigation. [Extracted from the article]

Objective: The present study investigates skill transfer from Virtual Reality (VR) sports training to the real world, using the fast-paced sport of table tennis. Background: A key assumption of VR training is that the learned skills and experiences transfer to the real world. Yet, in certain application areas, such as VR sports training, the research testing this assumption is sparse. Design: Real-world table tennis performance was assessed using a mixed-model analysis of variance. The analysis comprised a between-subjects (VR training group vs control group) and a within-subjects (pre- and post-training) factor. Method: Fifty-seven participants (23 females) were either assigned to a VR training group (n = 29) or no-training control group (n = 28). During VR training, participants were immersed in competitive table tennis matches against an artificial intelligence opponent. An expert table tennis coach evaluated participants on real-world table tennis playing before and after the training phase. Blinded regarding participant's group assignment, the expert assessed participants’ backhand, forehand and serving on quantitative aspects (e.g. count of rallies without errors) and quality of skill aspects (e.g. technique and consistency). Results: VR training significantly improved participants’ real-world table tennis performance compared to a no-training control group in both quantitative (p < .001, Cohen’s d = 1.08) and quality of skill assessments (p < .001, Cohen’s d = 1.10). Conclusions: This study adds to a sparse yet expanding literature, demonstrating real-world skill transfer from Virtual Reality in an athletic task. [ABSTRACT FROM AUTHOR]

The tennis Grand Slam tournaments play a key role among the major sport events. Sport has also got a social interest to strive for justice. Is the main draw always fair? Is the competition format system right? Overall: can we achieve a just final result? When answering these questions, we need to focus on the telos of the sport event. Present study shows the relating theories of justice and examines them in connection with the US Open: from the evolutionist conception, through Aristotle's excellence-based justice theory, to egalitarianism, meritocracy, equity and it also analyses some issues around positive discrimination. The study examines the justice theories of the US Open 2017 Men's Singles Tournament's with special focus on the draw, the competition format system and the final result. An important point: we can only talk about justice if it is consistent with the telos of the event – this is an exclusion criterion. In addition to the systematic processing of justice theories, the research is based on the International Tennis Federation's (ITF) official documents and on the case study: the official competition regulation and final result of the US Open 2017 Tournament. As an outcome of the research, we can conclude that several theories of justice appear in accordance with the telos of the US Open 2017 Tournament. Each element, namely the draw, the competition format system and the final result can be fair, however, they all depend on the applied theory of justice. Which theories should be applied in certain cases and why? The research also confirms that certain theories of justice do not match the telos of the US Open Grand Slam Tournament. These theories cannot be applied in certain cases. For future search areas we can examine other justice theories, or other related tennis event's justice. [ABSTRACT FROM AUTHOR]

Tennis is a very popular sport in the world. Many researchers have worked in the fields of forecasting the outcome of tennis matches using past statistical data records. This paper mainly investigates the comparison between three different classifiers namely decision tree, learning vector quantization and support vector machine. The research study aims to predict the result of tennis singles matches using eight UCI databases of grand slam tennis tournaments and evaluate the classification performance using various measures such as the root-mean-square error, accuracy, false positive rate, true positive rate, kappa statistic, recall, precision, and f-measure. All these performance measures confirm the supremacy of the decision tree classification algorithm compared to the others. [ABSTRACT FROM AUTHOR]

Background: Tennis players perform a large number of multidirectional and cutting movements, together with asymmetrical rotational motions resulting from serves and groundstrokes. Numerous shot repetitions and multidirectional motions directly influence a tennis player's upper and lower extremity joint range of motion (ROM). Objective: This study evaluated the changes in the range of motion of junior tennis players before and after match play. Methods: Twelve male (age 14.4 ± 1.3 years) and twelve female (age 13.4 ± 2.1 years) junior tennis players participated in the study. Two skilled experts performed 13 tests to measure passive range of motion of the dominant and non-dominant shoulder, elbow, wrist, hip, knee, and subtalar joints, before and after match play. The t-test and Wilcoxon test were used to determine the differences between the ROM before and after the tennis match, and the differences between the dominant and non-dominant sides of the body. Results: Bilateral measurement of the internal rotation of the shoulder joints, forearm pronation, and inversion of the subtalar joints before match play, show significant differences between extremities, similarly as the elevation of the arm in the coronal plane and forearm pronation, after a tennis match, were also found to display statistically significant differences. ROM values were higher for the internal rotation of both shoulders, external rotation of the non-dominant shoulder, elevation of the arms in the coronal plane, flexion in the elbow joints, pronation in the forearms, adduction in the hips, as well as eversion and inversion of the subtalar joints. Conclusions: Male and female junior tennis players increase their joint ROM during match play through motions which are involved in the execution of tennis shots and tennis movement patterns. Tennis matches that last 90 minutes or less do not have a negative impact on the flexibility of young tennis players. [ABSTRACT FROM AUTHOR]

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Introduction: A tennis player has a very limited time to hit an incoming ball; however, the ball delivery time is affected by playing on different surfaces. Consequently, the playing surface can affect also other match characteristics as players can reach more incoming balls or can move on the court with different intensity (cover more distance). Aim of Study: The aim is to analyze the rally pace characteristics and the frequency of rally shots in men's matches in the Australian Open, French Open and Wimbledon in 2017. Material and Methods: We analyzed 24 male matches in the Australian Open, French Open and Wimbledon in 2017. Analysis of variance including post-hoc tests and Cohen d were used to compare the point duration, number of rally shots, time between the points, rally pace and work to rest ratio among these tournaments. Results: The rally pace (mean ball flight time between the opponents) was the fastest in the Australian Open (1.22 s) and was significantly faster (p=0.003) compared to the French Open (1.35 s). The rally pace in the Wimbledon reached 1.27 s and Cohen d showed large effect between the rally pace in the Wimbledon and French Open or moderate effect between the Australian Open and Wimbledon. There were other differences among the tournaments, but the lowest number of rally shots (4.07), point duration (5.30 s) and time between points (18.82 s) was reached in the Wimbledon. More than 50 % of all points were finished within the first four shots (most in the Wimbledon - 66%). Conclusion: These findings show and endorse the impact of surface differences on the game performance in professional tennis and can be used to shape specific training sessions on different surfaces. [ABSTRACT FROM AUTHOR]

Tennis matches are hierarchies made up of sets containing games which, in turn, contain points. Traditional tennis games and tiebreakers could theoretically be infinite in length because a player needs to be at least 2 points ahead of the opponent to win. Fast4 tennis is a newer format of tennis that has been used at a number of levels of the sport including professional tennis where it has been used in Next Generation Finals events since 2017. The purpose of the current investigation is to compare the traditional tennis format to Fast4 tennis in terms of the probability of different players winning matches and the duration of matches. Probabilistic models of Fast4 tennis games and tiebreakers were developed. These models allowed the probability of winning games and tiebreakers to be compared between the two formats of tennis for a range of probabilities of players winning points. The models were then used within a series of simulations to determine the probability of winning sets and matches as well as the durations of games, tiebreakers, sets and matches in the two formats. Each component of the two formats of tennis was simulated 100,000 times revealing a reduced impact of serve, greater chance of upsets and shorter matches in Fast 4 tennis than in traditional tennis. The probability of players of differing abilities winning matches as well as the duration of tennis matches should be considered by those making decisions on the format of matches to be applied in tennis tournaments as well as by those preparing to compete in such tournaments. [ABSTRACT FROM AUTHOR]

Background: A few studies have shown that different types of court surfaces can have different effects on tennis match performance in different age groups, however, no studies have researched on tennis match performance responses in young tennis players. Objective: The purpose of this study was to evaluate the effect of different court surfaces on psychophysiological responses, time-motion and match characteristics of young tennis players. Methods: Twenty-six young male tennis players (age 13.0 ± 0.3 years, body height 158 ± 8 cm, body mass 48 ± 7 kg) volunteered to participate in the study. Heart rate was monitored along with total distance covered in four different speed zoneswalking, low-intensity running, moderate-intensity running and high-intensity running, using two portable multivariable integrated 10 Hz GPS monitoring devices over twenty-six outdoor tennis matches; ratings of perceived exertion and enjoyment level were also determined at the end of the matches. Variables describing the characteristics of the matches determined from video recordings were: strokes per rally, rally duration, effective playing time, work-to-rest ratio and rest time between rallies. Differences between hard and clay courts were assessed by a paired t-test. Results: The results showed that clay court surfaces induced significantly more perceived enjoyment scores (29.4 ± 2.8 vs. 26.0 ± 3.2) with lower perceived exertion level (13.4 ± 2.7 vs. 14.4 ± 2.9) compared to hard courts. Moreover, a clay court surface is also more effective at improving physiological responses, time-motion and match characteristics compared to hard court. Conclusions: If a coach strives to improve their young tennis players' tennis-specific performance with greater physical enjoyment, clay court surfaces should be specially used in their tennis training season. [ABSTRACT FROM AUTHOR]

This article has been retracted by Hindawi following an investigation undertaken by the publisher [[1]]. We wish to credit our own Research Integrity and Research Publishing teams and anonymous and named external researchers and research integrity experts for contributing to this investigation. Wiley and Hindawi regrets that the usual quality checks did not identify these issues before publication and have since put additional measures in place to safeguard research integrity. [Extracted from the article]

In many sports contests, the equilibrium requires players to randomize across repeated rounds, i.e., exhibit no temporal predictability. Such sports data present a window into the (in)efficiency of random sequence generation in a natural competitive environment, where the decision makers (tennis players) are both highly experienced and incentivized compared to laboratory studies. I resolve a long-standing debate about whether professional players' tennis serve directions are serially independent (Hsu, Huang & Tang, 2007) or not (Walker & Wooders, 2001) using a new dataset that is two orders of magnitude larger than those studies. I examine both between- and within-player determinants of the degree of serial (in)dependence. Evidence of the existence of significant serial dependence across serves is presented, even among players ranked Number 1 in the world. Furthermore, significant heterogeneity was found with respect to the strength of serial dependence and also its sign. A novel finding is that Number 1 and Number 2 ranked players tend to under-alternate on average, whereas in line with previous findings, the lower-ranked the players, the greater their tendency to over-alternate. Within-player analyses show that high-ranked players do not condition their randomization behavior on their opponent's ranking. However, the under-alternation of top players would be consistent with a best-response to beliefs that the population of opponents over-alternates on average. Finally, the degree of observed serial dependence is not systematically related to other match variables proxying for match difficulty, fatigue, and psychological pressure. [ABSTRACT FROM AUTHOR]

The aim of our study is to compare selected game characteristics on different surfaces among all grand-slam tournaments and between male and female professional tennis players. We analyzed match characteristics from all grand-slam tournaments - Australian Open, French Open, Wimbledon and US Open. We had data from all the matches and tournaments (127 singles matches from male and 127 female singles matches per each tournament). We compared the tournaments and also the genders. The data of the match characteristics were obtained through the official tournaments websites. The results showed women won significantly more return games compared to men (by 12%); men won significantly more points after 1st and 2nd serve compared to women (by 7% or 6% respectively); men played significantly more games per set; and women played significantly more points per game. Faster surface provides greater advantage to the server. Therefore it is important to practice serves prior these tournament. The least percentage of winners was reached at US Open. The mean percentage of 2nd serve points won in women's matches reached only 45%, therefore receiving the 2nd serve could be an advantage in women's tennis. The receiver should use this advantage by a good return. [ABSTRACT FROM AUTHOR]

We propose a logistic regression model to predict the win probability in a tennis match in the context of the betting market. The variables included in the model are ATP points and rankings, the players' ages, the home factor and the information derived from bookmaker odds. The model is estimated using data related to 2012 tournaments, and it is then used in an out-ofsample betting experiment where the odds implied by the model are used, following a specific procedure, for betting against bookmakers. The algorithm is applied to all matches of the four Grand Slam Championships 2013, and the whole procedure is evaluated with respect to the global return of the strategy. After 501 matches, the total cumulative return is 16.3%. [ABSTRACT FROM AUTHOR]

Team Tennis competitions produce aggregate scores for teams, and thus team rankings, based on head-to-head matchups of individual team members. Similar scoring rules can be used to rank any two groups that must be compared on the basis of paired elements. We explore such rules in terms of their strategic and social choice characteristics, with particular emphasis on the role of cycles. We first show that cycles play an important role in promoting competitive balance, and show that cycles allow for a maximum range of competitive balance within a league of competing teams. We also illustrate the impact that strategic behavior can have on the unpredictability of competition outcomes, and show for a general class of team tennis scoring rules that a rule is strategy-proof if and only if it is acyclic (dictatorial) and manipulable otherwise. Given the benefits of cycles and their relationship with manipulability, a league valuing competitive balance may invite such social choice violations when choosing a scoring rule. [ABSTRACT FROM AUTHOR]

We identify professional tennis matches where one player competes for extraordinarily high payoffs while their opposition does not. Players 'on the bubble' of direct qualification to upcoming Grand Slam events face substantially higher stakes than opponents, which presents an opportunity for collusion. Our findings produce evidence that is consistent with the hypothesis of unethical behavior taking place on the men's tour, as bubble players are 5.1 percentage points more likely to beat better ranked opponents than in comparable nonbubble matches. However, no such evidence emerges when analyzing women's tennis. We find additional support for the hypothesis of match-fixing activities on the men's tour from analyzing the occurrence of tie-breaks and the fact that our results become stronger once monetary incentives were increased after the 2013 season. Finally, the betting market does not predict this phenomenon, further confirming our suspicion of irregular activities. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare activity patterns between male and female wheelchair tennis (WT) matches. Sixteen singles international WT matches (eight male and eight female) were analysed. Each match was recorded and analysed according to the following variables: total match time (minutes), total set time (minutes), effective playing time (%), total resting time (%), working timetresting time ratio (W:R), resting time between points (seconds), rally duration (seconds), points per set, shots per set, shots per rally, bounces per point, and time between shots (seconds). Mann-Whitney U test was used to compare between the genders and Wilcoxon test was used to compare variables with the type of point (non-game point opportunity-NGO, and game point opportunity - GO). Female matches showed higher values (p<.05) in rally duration, bounces per point, and frequency of shots than male matches. Both genders spent more time between points in GO than in NGO situation. The findings indicate that male and female players play in a different way, and these differences should be taken into consideration by the WT coaches. [ABSTRACT FROM AUTHOR]

Sports video research is a popular topic that has been applied to many prominent sports for a large spectrum of applications. In this paper we introduce a technology platform which has been developed for the tennis context, able to extract action sequences and provide support to coaches for players performance analysis during training and official matches. The system consists of an hardware architecture, devised to acquire data in the tennis context and for the specific domain requirements, and a number of processing modules which are able to track both the ball and the players, to extract semantic information from their interactions and automatically annotate video sequences. The aim of this paper is to demonstrate that the proposed combination of hardware and software modules is able to extract 3D ball trajectories robust enough to evaluate ball changes of direction recognizing serves, strokes and bounces. Starting from these information, a finite state machine based decision process can be employed to evaluate the score of each action of the game. The entire platform has been tested in real experiments during both training sessions and matches, and results show that automatic annotation of key events along with 3D positions and scores can be used to support coaches in the extraction of valuable information about players intentions and behaviours. [ABSTRACT FROM AUTHOR]

This paper addresses automatic video summarization. We propose a novel approach that relies on constraint satisfaction programming (CSP). An expert defines the general rules for summary generation. These rules are written as constraints. The (final) user can define additional constraints or enter high-level parameters of predefined constraints. This has many advantages. It clearly separates summary generation rules from the summary generation algorithm (the CSP solver here). The summary can hence be modified without reviewing the whole generation process. It also allows users to adapt the summary to the target application and to their preferences. The proposed approach is mainly dedicated to edited professional video (like TV programs). It has been extensively evaluated not only using objective measures but also through a large-scale user evaluation. This evaluation involved more than 60 people. Experiments have been performed within the challenging application of tennis match automatic summarization, using about 28.5 h of videos. [ABSTRACT FROM PUBLISHER]

The purpose of this study was to analyse differences in rally length considering attack effectiveness, a players' location and a game outcome in professional padel players. A total of 1527 rallies from 10 male matches of the 2013 Masters Finals of the World Padel Tour were registered through systematic observation. Data treatment included non-parametric mean comparisons (Mann-Withney and Kruskal-Wallis tests), and association analyses (crosstabs and Chi square analysis). In overall, 40% of unforced errors were made within the first 4 s of the rally, over 50% of points were scored between the 5th and 11th s, and 30% of forced errors occurred after the 11th -s of the rally. Hence, the ability to score in rallies of over 11 s duration and not making unforced errors within the first 4 s contributed to the rally outcome. More specifically, winners played longer rallies compared to losers (10.42 ± 7.77 s vs. 8.42 ± 6.43 s); particularly at the net, when scoring from the baseline (11.04 ± 7.64 s vs. 8.90 ± 5.41 s) and making forced (8.86 ± 7.44 s vs. 6.86 ± 6.24 s) and unforced errors (11.91 ± 9.47 s vs. 8.33 ± 6.92 s). Such knowledge may have implications in the design and structure of specific training programmes for padel players according to competition requirements. [ABSTRACT FROM AUTHOR]

The aims of this study were: a) to investigate the game temporal structure in high-level table tennis competitions; b) to verify the influence of game evolution in international competitions from 2009 to 2012 (World Table Tennis Championships and the Olympic Games) on game temporal structure; c) to compare game temporal structure according to the phase of competition. Comparisons between the three international tournaments demonstrated that rally duration decreased significantly (p < 0.05) during the analyzed period (2009-2012), while the rest time increased (p < 0.05) from 2009 to 2011, but decreased (p < 0.05) from 2011 to 2012. In the competition phase analysis, it was found that rally duration decreased (p < 0.05) in the quarterfinals in relation to the semifinals and finals, while the rest time increased (p < 0.05) from the quarterfinals to semifinals and finals. Based on our findings and previous literature, we concluded that the performance level, game evolution and the competition phase influenced the game temporal structure of table tennis, considering longer rest periods adopted by elite athletes in relation to non-elite athletes, the reduction in rally duration and an increase in rest time over the 2009-2012 period and through the competition phases (quarterfinals to finals). [ABSTRACT FROM AUTHOR]