Moshing came from the Psychobilly and Punk crowd.
Psychos call it wrecking and it's been around for a lot of years now , I once got a black eye about 10 seconds after getting on the floor.
Rules of Wrecking are:
Have fun
Never try to injure another wrecker
If someone falls then the nearest people pick him up .
Anyone trying to cause injuries is forced out.
If you can't take it don't get in.

Safe Wrecking everyone, you can call it moshing if ya want but it will always be The Mutant Wrecking Krew for me.