OBJECTIVE: To test a helmetless-tackling behavioral intervention for reducing head impacts in National Collegiate Athletic Association Division I football players. DESIGN: Randomized controlled clinical trial. SETTING: Football field. PATIENTS OR OTHER PARTICIPANTS: Fifty collegiate football players (intervention = 25, control = 25). INTERVENTION(S): The intervention group participated in a 5-minute tackling drill without their helmets and shoulder pads twice per week in the preseason and once per week through the season. During this time, the control group performed noncontact football skills. MAIN OUTCOME MEASURE(S): Frequency of head impacts was recorded by an impact sensor for each athlete-exposure (AE). Data were tested with a 2 × 3 (group and time) repeated-measures analysis of variance. Significant interactions and main effects (P < .05) were followed with t tests. RESULTS: Head impacts/AE decreased for the intervention group compared with the control group by the end of the season (9.99 ± 6.10 versus 13.84 ± 7.27, respectively). The intervention group had 30% fewer impacts/AE than the control group by season's end (9.99 ± 6.10 versus 14.32 ± 8.45, respectively). CONCLUSION: A helmetless-tackling training intervention reduced head impacts in collegiate football players within 1 season.