Baseball fans in Baltimore have not had much to cheer about in recent years. The Orioles have won fewer than 70 games in each of the last five seasons. The last time they finished the season without a losing record was 1997 (when they won 98 games and took first in the division). Basically, for the last 14 seasons these guys have sucked.
So it is almost understandable when a young fan might become a little overzealous in his attempt to have a good time at the ball game. Add a few beers and it is entirely plausible that a fan might be willing to do something a little crazy for his/her own entertainment and for the entertainment of the fans--like jump the outfield wall and run around the field like an idiot.