In OJ's "confession" he taped for Fox awhile back his version is that he squared up with him and took on a karate stance. He alluded to that being what caused his aggression toward him.
Most people here would have been like woah I'm out, not squared up to fight, regardless of what was going on. That being said his confession has changed versions twice if you cross reference it against his unofficial confession he made to a friend, so he's not very credible. I could def see a guy squaring up though and trying to get involved despite not really knowing the situation. Seems plausible.