Moral disengagement (MD) has been positively associated with antisocial behavior (AB) in sport. However, the longitudinal associations between MD and AB are unexamined to date. Adopting a three-wave cross-lagged panel design, the authors examined the reciprocal relations between MD and two forms of AB (i.e., toward opponents and teammates) across a competitive season with a sample of 407 team-sport athletes (M age = 15.7 years) from Canada. Using structural equation modeling, the authors found strong positive autoregressive effects for MD and both forms of AB across both time periods. They also identified strong positive synchronous correlations between MD and both types of AB at each time point. Finally, cross-lagged effects were only found between MD and AB toward opponents; effects from MD to AB toward opponents were stronger than the reciprocal effects. These findings contribute important knowledge on the regulation of AB in sport.