International Journal of Human Movement and Sports Sciences 10(2): 338-342, 2022 http://www.hrpub.org DOI: 10.13189/saj.2022.100226 Validity and Reliability of Reactive Agility Measurements of Tennis Performance Wisnu Nugroho, Tomoliyus * , Abdul Alim, Fauzi, Hari Yuliarto Department of Sport Science, Yogyakarta State University, Indonesia Received January 31, 2022; Revised April 8, 2022; Accepted April 21, 2022 Cite This Paper in the following Citation Styles (a): [1] Wisnu Nugroho, Tomoliyus, Abdul Alim, Fauzi, Hari Yuliarto , "Validity and Reliability of Reactive Agility Measurements of Tennis Performance," International Journal of Human Movement and Sports Sciences, Vol. 10, No. 2, pp. 338 - 342, 2022. DOI: 10.13189/saj.2022.100226. (b): Wisnu Nugroho, Tomoliyus, Abdul Alim, Fauzi, Hari Yuliarto (2022). Validity and Reliability of Reactive Agility Measurements of Tennis Performance. International Journal of Human Movement and Sports Sciences, 10(2), 338 - 342. DOI: 10.13189/saj.2022.100226. Copyright©2022 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract Reactive agility measurement tool recently has become one of the important issues in the physical training for tennis performance. Therefore, finding a valid and reliable reactive agility measuring instrument for tennis performance is needed. This study aimed to do a validity and reliability test of the reactive agility measuring instrument for tennis performance. This study used a mixed-methods approach. The seven experts participants were determined by the criteria of an evaluation expert and a tennis expert, or both. This study had three stages. The first was document analysis (international journal). It is used to develop a construction design for the reactive tennis agility measuring instrument. The second stage was content validation. The participants were seven experts. Then, the data collection technique used the Delphi technique. The research instrument uses a scale of one to four, namely very relevant, relevant, less relevant, and irrelevant. The data analysis used the Aiken formula for content validity and Reliability Analysis between raters using ICC. The first stage of research results has found the operational definition of reactive agility tennis: the ability to move in seconds after receiving a stimulus. In addition, the "Y" shape construction design of the reactive tennis agility measuring instrument has been arranged. The second stage resulted in the contents validation of a large tennis reactive agility measuring instrument. The third stage found the reliability between raters of a large tennis reactive agility measuring instrument. Keywords Tennis, Content Validity, Reactive Agility Measuring Instrument 1. Introduction Tennis is an intermittent sport that requires acceleration for changing the direction, reaction, and balance for repeated and varied strokes, such as different ball speeds, varying ball spins and moving at various field angles. Tennis athletes require very fast neuromuscular coordination in responding to the ball [1,2]. Neuromuscular coordination requires reaction speed, agility, balance, and coordination [3,4,5]. Therefore, tennis coaches need a training program and a measuring instrument to measure the elements of reaction, agility, and balance, which is called reactive agility. Reactive agility measuring instrument can be described as the ability to adjust the motion change as quickly as possible and maintain balance in responding to a stimulus [6]. However, many tennis available reactive agility measurement tools cannot measure the movement of holistic tennis skills. Therefore, a valid and reliable reactive agility measurement instrument is needed to assess reactive tennis agility accurately. Sheppard et al. [7] have researched developing a reactive agility measurement instrument for football. The results showed that the reactive agility test was valid and reliable for football. Morland et al. [8] also researched the development of a reactive agility test for hockey. The results showed that the reactive agility test was valid and reliable for hockey. In addition, Yudistira and Tomoliyus have conducted research on developing a reactive agility test in karate. The results showed that the reactive agility test in karate has high content validity and high inter-rater