Basically, Iron Maiden were closing the show in LA, but while doing so were pelted by eggs and bottle caps, as well as actually being spat at, by a group of people wearing Ozzfest laminates. The stage was invaded/rushed by members of the Osbourne-affiliated Black Label Society, and the PA was switched off six times during their set. Prior to their set, Sharon and daughter Kelly were seen encouraging people to join them in throwing eggs, etc, at Iron Maiden. Sharon later called Bruce Dickinson a prick in front of the 40,000-person crowd.
The above is just a summary from an account on metal site Blabbermouth.net, which can be found right here and subsequent (comical) fallout here.