It appears the fan was clowning around when he fell.
Luckily he wasn’t seriously hurt. According to Deadspin he just hurt his shoulder, but the person he fell on had a pretty serious head injury.
@WGRZ this is the "jumper" pic.twitter.com/u6C6z4DALL
— jack mehoff (@jacksessionn) November 17, 2013
Don’t play around in the stands. This guy is lucky he isn’t dead or killed someone.