Plenty of times in CZW 1999 - 2003, hence monthly injuries and firings.
As Raz posted, in June 2008 IWA-MS had one incident where guys backstage thought Mike wasn't pulling his strikes enough against Mickie Knuckles, but I'm sure MK was over selling.
Anyway, dudes from behind the curtain ran out and bludgeoned Levy in front of the ref, who let it go. Levy was literally unconscious so that he couldn't 'shoot' against Knuckles. One of the run-in wrestlers' children bragged about poking Levy Jackass style with a broom handle as he limped backstage.
Kayfabe lives in CZW! Beat up one of them, and you must beat up the entire roster.
http://ireport.cnn.com/docs/DOC-54605