Adequacy of standards for kick impact in the Taekwondo electronic scoring system: Comparison of a reference group model based on empirical data


 Background: In Taekwondo competitions, the rule is that points are scored when the impact of the kick reaches a predetermined threshold of strength. This study aimed to explore the adequacy of the protector and scoring system (PSS) designed to determine Taekwondo body scoring based on a reference group model (RGM). Specifically, the kicking impact of the PSS was calculated using data from 188 matches fought during of 2018 Jakarta Asian Games. The RGM was designed based on empirical data by classifying the victory and defeat groups by gender and weight class, and the scoring method was set according to these criteria. Result: The result of this study are as follows. First, there was no difference in the average impact of kicks of Taekwondo players by weight class. Second, as a result of setting up the kick scoring impact standards of Taekwondo PSS by classifying the winning and non-winning groups, the kickscoring impact set by the WTF was found to be high in all weight classes except -58 kg.Lastly, as a result of comparing the settings of impact to score according to weight classes, the kick scoring impact standard set by the WTF was higher in heavyweight (men's: under-80kg, +80kg, women's: under-67kg, over-67kg) than in the lightweight (men's: under-58kg, under-63kg, under-68kg, women's: under49kg, under53kg, under 57 kg). Conclusion: The kick scoring impact set by the WTF was found to be high in all weight classes except for the under 58 kg class, as a result of defining kick scoring impact based on the standards of WTF-certified PSS by classifying the matches into winning and non-winning groups. Finally, as a result of comparing the scoring impact settings according to weight class, the kick scoring impact standard set by the WTF was higher for the heavier weight classes than for the lighter weight classes.


Introduction
Taekwondo is a sport that attracts many people and it is becoming a popular sport practiced worldwide.
Furthermore, Taekwondo was adopted as an Olympic sport where only the best athletes participate. In this regard, the World Taekwondo Federation (WTF) is making various efforts to improve the sport of Taekwondo, for example by assessing the fairness of the scoring system which is a currently an issue in Taekwondo competitions. Changes in the scoring method are being implemented to ensure fairness in Taekwondo matches. In the past, the scores were determined based on the subjective judgment of the referees (Cho & Eom, 2007).
However, the protector and scoring system (PSS) was developed and introduced in order to addressproblemswiththe scoring method encountered in the past. PSS sets scoring criteria according to the kick impact determinedin advance formale and female weight classes, and automatically calculates the score when the scoring area is hit harderthan the set kick impact threshold (World Taekwondo Federation, 2019). The bene t of setting a kick impact scoring thresholdis that the higher the weight class, the higher the kick impact standard. In this regard, Taekwondo is applying a more objectiveand consistent scoringtool than in the past (Cho, Jung, Kang, Kim, & Kwak, 2009), contributing to its becoming a global sport.
validityof the kick impact scoring standard remains unclear, even though its objectivity and consistency were improved. Currently, the WTF has arbitrarily set the kick impact scoring scalefor maleand femaleweight classes under an expert's subjective judgment (Lee, 2016). Furthermore, it is necessary to establish the basis for different impact settings,according to weight class. For example, in the case of males, the scoring impact of the under-58kg weight class was set to 18 levels, that of the under-63kgweight class was set to 20 levels, and that of the under-68kgweight class was set to 21 levels.
Despite the same 5 kg difference, the under-58kg and under-63kgweight classes have a difference of twolevels, while the under-63kg and under-68kgweight classes have a difference of one level (Choi & Jeon, 2019). These differences in setting kick impact leads todoubt inboth the players and the coaches. In fact, a difference of one level is not great, but due to the nature of Taekwondo, where the criteria for judging scores are based on a reference-oriented evaluation, itcould lead to skewedresults. Moreover, studies on setting kick scoring impact are continuously requiredbecause it can be an important factor affecting score, game ow, and player results. Research on Taekwondo  . Thus, studies on setting kick scoring impact arerequired. This study aimedto con rm the adequacy of setting akick impact standard forTaekwondo PSS. Speci cally, we analyzed the difference between the kick impact standard set by the WTF and the kick impact standard based on kick impact data fromthe 2018 Jakarta Asian Games. Duringthis process, weveri ed whether the kicking standard currently applied was high or low.

Research Data
In this study, the adequacy of akick impact standard by weight class was con rmed using 2018 Jakarta Asian Games Taekwondo

DataAcquisition Procedure
In this study, data from KP&P PSSobtainedin the 2018 Jakarta Asian Games Taekwondo matcheswere provided by the Asian Taekwondo Federation and KP&P. This is a score that can be publicly con rmed as the PSS score generated in the game. The KP&P PSS is an o cial accreditation body certi ed by the WTF (October 23, 2012) and it is the o cial scoring system used in world competitions and Asian Games.
Only the scoring impact generated in the trunk area was entered and classi ed by weight classin order to use the data forthe scoring impact calculated by KP &PPSS as research data. Data was input by threeTaekwondo match analysis experts to minimize error. Several matches were randomly selected and re-recorded to con rm the match with the previous record,after enteringthe data. The PSS kicking impact calculated through this process was 2,286 times for men (scoring frequency: 814 times, effective hit frequency: 1430), and 1,389 times for women(scoring frequency: 650 times, effective hit frequency: 688 times), and these values were used as research data.

Group Classi cation for Establishing Kick Impact Reference Pointsfor the Protector and Scoring System
Thecriterion groups model, one of the empirical methods, was usedin this studyto con rm the adequacy of the Taekwondo PSS kick impact reference point. The reference group model is divided into the group that meets the criteria and the onthat does not. The intersection point of the distribution of scores of the two groups was set as the reference point (Popham, 1990). Therefore, twomethods were used in this study to classify the group to determine the appropriateness of the kick impact reference. First, the winning group (which met the criteria) and the non-winning group (which did not meet the criteria), according to weight category, were divided and compared with the reference point shown at the intersection point of the 2-group score distributions with the kick impact reference point currently applied by WTF. Then, after classifying the groups according toweight class, the score distribution intersection point was identi ed.
For example, for men's weight classes, the current kick impact reference point is determined by checking and comparing the intersection of the score distributions for the twogroups in the following order: under-58kg, and under-63kg, under-63kg and under-68kg, under-68kg and under-80kg, under-80kg, andover-80kgweight classes.

Data Processing Method
The descriptive statistics forthe PSS kick scoring impact were calculatedby weight class. Cutoff scores were calculated to establish scoring criteria according to the reference group. The cutoff score was calculated based on the standard normal distribution using the mean and standard deviation of the kicking intensities of the winning and non-winning groups according togender and weight. Furthermore, the intersection of the kicking intensity distributions of the winning and non-winning groups was selected as the cutoff score (Kaftandjieva, 2010 Table 4 showsthe kick impact criteria of the PSSaccording to men's and women's weight classes. Weight class was divided based on weight classin order to set the kick scoring impact. As a result, for men under58kg and under63kg, 21 levels (acc:.622), under63kg and under68kg, 21 levels (acc:.492), under68kg and under80kg, 22 levels, and under80kg and over 80kg, 21levels (acc:.502). Forwomen, under49kg and under53kg, 15 levels (acc:,468), under53kg and under57kg, 19 levels (acc:.610), under57kg and under67kg, 17 levels (acc:.448), and under67kg and over67kg, 18 levels (acc:.572). When dividingthe kick scoring impactinto weight classes, it was found to be higher than the kick scoring impact currently applied in most heavyweight classes.

Discussion
The introduction of PSS to Taekwondo was attractive to many coaches, athletes, and researchers. PSS is a measuring tool that determines whether a player scores during a match. Research onthevalidity and adequacy of the tool has been conducted continuously (Morrow, Mood, Disch, & Kang, 2015). However, the criteria for determining the score in PSS, that is, research on the setting of the kick score impact is insu cient. Currently, the kick score impact setting is set by subjective judgment, thus leaving doubts.
Therefore, this study was performed to con rm the adequacy of the setting of the impact of the kick protector for PSS.
First, as a result of con rming the form of impact of the PSS kick according to men's and women's weight class, it was con rmed that both men and women have similar patterns regardless of weight class.
Especially, when comparing the average kick impact by weight class, it was determinedthat the difference in kick impact was not signi cant. In the current WTF guidelines, the scoring impact for kicks is set higher for higher weight classes. Previous studies also reported that scoringfrequency was relatively low inhigher weight classes than in lower weight classes, pointing to the same problem of setting the scoring strength forkicks (Choi & Jeon, 2019).
Furthermore, this study utilizes survey data to calculate and compare the PSS kick scoring impact reference point. As a result, it was con rmed that in both methods of calculating the reference point, the weighted kick score setting was set higher than the currently set kick score. In fact, it is generallymore logical to set a higher kick scoring impact for ahigher weight class. However, considering that there is movement of the opponent player when being kicked and the kicks are defended by hand, setting a graded kick scoring impact isamatter of concern.
On the other hand, the kick scoring impact criteria suggested in the study results and the kick scoring impact set by the WTF differs by4 levels to 1 level. In fact, although a 1-level difference might seem small, it can still affect the score, and accordingly change the result. Since Taekwondo has such characteristics, it is inevitable to emphasize the importance ofsetting the kick scoring impact of PSS.
Finally, the kick scoring impact setting in men's and women's different weight classes isdependent on the method and, thus, the limitations were that there are no clear standard of setting kick scoring impact (e.g.
the kick scoring impact standard was under53kg: 15levels, under57kg: 17 levels, and under67kg: 16 levels, showing that higher weight classes havealower standard of kick scoring impact). In addition, only the Asian Games data wereused, which can be interpreted as results for speci c regions. Nevertheless, it is certain that this study provides basic data that could solve the problem of setting the kick scoring impact suggested by the WTF. Also, this study attempted to identify the problem and solve it by using nonsubjective data in setting the kick scoring impact, which may be used as important information in the future. Subsequent studies should focus on experts setting kick scoring impact according to the data results, whichcould be used as a more valid measure of athleticperformance.

Conclusion
This study con rmed the adequacy of setting the scoring impact of Taekwondo