After getting picked off trying to steal a base in the top of the 8th inning of a 7-5 win over the Rockies, the high-priced outfielder lost his cool in the dugout and slammed his helmet, which ricocheted off the ground and hit Alonso in the head.
Several Padres players rushed to their fallen teammate, who got up in an even worse mood than Upton and knocked down some buckets of gum in frustration. Alonso was then pulled from the game as a precautionary measure.
After the game, Upton took full responsibility for his actions. "It's childish. I've got to do better than that and not make that mistake again," he said, via MLB.com.