Rago, V, Brito, J, Figueiredo, P, Ermidis, G, Barreira, D, and Rebelo, A. The arrowhead agility test: Reliability, minimum detectable change, and practical applications in soccer players. J Strength Cond Res 34(2): 483-494, 2020-Four independent studies were conducted to examine the utility of the arrowhead agility test (AAT) to measure change of direction (COD) capacity in soccer players, specifically, (a) intersession reliability and minimum detectable change (n = 24); (b) power-dependent abilities associated with AAT performance (n = 56); and (c) fatigue sensitivity (n = 20); differences between competitive levels and age groups (n = 264). Irrespective of the AAT outcome measure (skillful side, less-skillful side, sum of both), intersession reliability and the ability to detect changes in performance were good (ICC = 0.80-0.83; CV = 1.25-2.21%; smallest worthwhile change, 0.06-0.12 >SEM, 0.01-0.03) except for the asymmetry index. A 15-m sprint explained a significant amount of variance in COD (p < 0.01; R = 0.42). Arrowhead agility test performance did not change from the prematch toward half time (p = 0.21). However, reduced COD performance was observed after an intense period in the second half and after the game, compared with prematch and half-time performance (p < 0.05; effect size [ES] = -0.85 to 0.42). Irrespective of age group, national players were more agile than regional players (p < 0.05; ES = -1.97 to -0.36). Moreover, independently of their competitive level, senior and U18 players had a better performance than U16 (p < 0.05; ES = -2.33 to -0.84), whereas no significant differences were observed between senior and U18. Percentiles were also reported in the results. The AAT is reliable to measure COD in soccer players. The test may simultaneously encompass 15-m sprint testing but should be implemented independently to countermovement jump. Furthermore, the test is sensitive to match-induced fatigue during the second half and discriminates players from different competitive levels.