## 1 Introduction  
Assessing the physical performance of youth athletes is crucial for talent identification, monitoring their development, and creating effective training programs [1, 2, 3, 4]. These evaluations help coaches and sports scientists identify the strengths and weaknesses of athletes, which can guide training decisions and optimize athlete development [5, 6, 7, 8, 9]. For athletes under 12 years of age (U12), a period characterized by rapid neuromuscular growth and motor skill development, reliable tests assessing their sprint speed, agility, and reactive agility are particularly valuable [4, 10]. During this critical developmental window, U12 athletes exhibit significant changes in their motor coordination and strength, making accurate assessments even more important [1]. These abilities, namely sprint speed, agility, and reactive agility, are essential in field-based sports, such as soccer, wherein athletes need to demonstrate quick linear speed, efficient directional changes, and the ability to react to dynamic game situations [11]. Reliable performance tests are fundamental for ensuring that observed changes in performance accurately reflect true developmental progress rather than measurement errors [12; 13; 14; 15]. High test-retest reliability ensures that repeated assessments yield consistent results, which is crucial for tracking an athlete's progress over time [16; 17]. Metrics like the intraclass correlation coefficient (ICC), coefficient of variation (CV), and standard error of measurement (SEM) are commonly used to determine the reliability of physical performance tests, with higher values indicating more reliable measurements [2; 18]. High test-retest reliability provides confidence that improvements or declines in performance over time are meaningful and are not due to measurement inconsistencies [17; 18]. Therefore, these tests can be used not only to monitor development, but also to guide individualized training programs, aimed at enhancing specific performance attributes [2; 15; 17]. Physical and cognitive demands in youth soccer require an integrated approach to training and assessment. Sprint speed, change of direction (COD), and reactive agility are crucial components that reflect both the athlete's neuromuscular qualities and their decision-making under pressure. Research has shown that performance in these domains is influenced not only by physical maturation [19] and anthropometric development, but also by functional movement quality [20], which can impact both the athlete's performance and injury risk. While pre-planned COD tasks rely heavily on strength and motor control, reactive agility incorporates cognitive processing and visual stimulus recognition, making it more representative of game-like situations [21]. Furthermore, involvement in structured training, such as soccer, has shown positive effects on motor function and postural control, even among special populations, such as children with intellectual disabilities [22], highlighting the broader benefits of sport-specific engagement. However, in pre-adolescent populations (e.g., U12 players), there is a lack of research exploring how these physical and perceptual motor abilities interact. Understanding these interrelationships can support more effective talent identification and the development of individualized training strategies in regard to youth soccer development programs. Based on the above-mentioned considerations, the primary objective of this study is to examine the relationships between sprint speed, COD, and reactive agility in U12 soccer players. Specifically, we aimed to investigate how linear sprinting performance (measured at 5 m, 10 m, and 15 m), the Modified Agility Test (MAT), and the Y-Shaped Reactive Agility (Y-SRA) test are correlated, in order to better understand the interaction between linear speed, COD ability, and perceptual cognitive agility in regard to soccer performance.