According to E! News, Patrick Schwarzenegger had obtained a fake ID to get into the club, and began to cause trouble when he was asked to step away from the DJ's set up.
A source explained the scene to US Weekly:
[Valadez] told him nicely a few times to please be careful because he kept bumping into it. ... I guess Patrick became annoyed so he started throwing ice at him. At this point one of the cocktail waitresses noticed it was Patrick Schwarzenegger and alerted the team who he was and that he was underage.
TMZ has video of Schwarzenegger outside the club, telling his friends he wanted to "beat the f**k out of the DJ":
Schwarzenegger later issued what seemed to be an apology for the incident on Twitter:
Excuse my language. I apologize— Patrick Shriver (@PSchwarzenegger) May 6, 2013
Live and learn, hope everyone has a blessed day— Patrick Shriver (@PSchwarzenegger) May 6, 2013