No prophylactic ankle stabilizer performance study has been conducted to date using high school football players, ie., players who are at risk of ankle sprains. In addition, the effect that prophylactic ankle stabilizer use has on performance by player position is unknown. The purpose of this study was to determine the effect of a semirigid and softshell prophylactic ankle stabilizer on performance by football player position in events testing vertical jump, speed, and agility. Twenty-five high school football players participated in the study. All subjects denied any history of ankle injury within 1 year of the study and previous experience with prophylactic ankle stabilizer use. Subjects completed three tests [vertical jump, 36.56-m (40-yd) sprint, and 18.28-m (20-yd) shuttle run] under three different ankle treatments: Aircast SportStirrup, DonJoy RocketSoc, and nonbraced control. Results of the study indicated that the Aircast SportStirrup and DonJoy RocketSoc, when compared with a nonbraced control, had no significant effect on vertical jump, 36.56-m (40-yd) sprint, and 18.28-m (20-yd) shuttle run performance. Skill players had faster 36.56-m (40-yd) sprint times than strength players regardless of ankle treatment. In conclusion, the Aircast SportStirrup and DonJoy RocketSoc did not facilitate or adversely affect performance involving vertical jump, speed, and agility of high school football players.