It isn't so much a backstage incident, because this real fight happened live on television. It was the first ECW One Night Stand pay per view, and Layfield among other WWE talents emerged in the ECW ring for the show closing brawl.
Right away, JBL had his eyes on The Meanie. As the brawl started, the WWE star walked over and started to pound his fist on Meanie's face. The result was blood and swelling instantly. The eye of Meanie full on shut due to swelling. JBL pounded some more before being pulled away. It was a shocking incident, a blatant disregard of the code between peers to protect each other in the ring. Bradshaw had been drinking heavily throughout the show, but this was plain uncalled for.
Vince McMahon didn't really care that much, and JBL got away with it - although Meanie would go on to pin his adversary in a 'revenge' match. The two reconciled and are now fine with each other.