Probably a 'noodle incident' that won't be actually explained fully unless it becomes a major plot point. Shouldn't be too hard to guess what happened, though. After all, there were a series of corp wars, including the one that led to the first Crash. And the normal corporate espionage, assassinations, etc. Any one of those incidents, stopped in part by a flashy Red Samurai that actually knew how to fight decently, would be a PR win that could make the board change them into an elite warrior group.