That's the LeBell incident I was talking about
It wasn't at "The Arnold", but at a film set and he didn't poop in his pants, but released his bladder. The guy who choked him out was the legendary Judo Gene LeBell
who was somewhat around 60 years old at that time and amongst martial artist a world renown grappler long before anyone outside Brasil ever heard of BJJ or the Gracies.
The story is confirmed by a guy who interviewed Bob Wall
who was present when the incident happened: