Morales hit a walk-off grand slam off Brandon League to end a 10-inning 5–1 victory over the Seattle Mariners at Angel Stadium of Anaheim on May 29, 2010. Approaching his celebrating teammates, he jumped up with the intention of stomping on home plate instead of simply stepping on it. His awkward landing resulted in a fracture in his lower left leg, placing him immediately on the disabled list. The injury required surgery, and he missed the rest of the 2010 season. In 51 games in the 2010 season, Morales hit .290 with 11 home runs and 39 RBIs.