Fellow coach lost his mind at practice yesterday. What would you do?

I am a community coach for the local 8th grade team . I am the only non-teacher coach on the staff. I witnessed something yesterday I have never seen in my days of playing and coaching. I started playing at age 6 and through graduation. I have been a HC/OC at the eighth grade level for 12 years prior to taking a break for a few years. My family and I moved to our current town 2 years ago and I got back in to coaching at the assistant level just because I missed being a coach. I have done my share of borderline discipline over the years. I have grabbed a few facemasks in the huddle and shook a player or two around by the shoulder pads but never physically assaulted a player.

Anyway, we were in a drill with about 12 players. It was myself, and two other coaches. The HC and 3 other coaches were across the field with other groups and did not see what happened. Only myself, one other coach and the players in our group.

One kid mildly back talked a coach by saying "I went the way you told me" in kind of a smart arse manner. The coach went ragebot like I have never seen. This kid, who weighs maybe 130 lbs was standing about 8 yards away. The coach screamed "don't ever back talk me again" with veins popping out of his neck and started on a dead sprint to the player. He ran right through him and pancaked the kid. I mean a legit whiplash type of pancake. Player went from vertical to horizontal in a millisecond. Then he stood over him screaming for a second and then reached down and jerked him up to his feet by his shoulder pads like a rag doll.

I was in shock. Coach made him run around the field the remainder of practice. I just looked at the coach and nodded my head at him like "damn dude!" and ran to catch up with the player to make sure he wasn't concussed or otherwise hurt. He was just really shocked and freaked out.

So, nobody but me and another coach saw this. The coach who went off has never exhibited this type of behavior before that I have seen. Should I tell the HC to be aware that he might have a big problem on his hand if the kids parents catch wind? Should I talk to the coach himself a day later and give him some friendly advice? As a community coach, i don't want to rock the boat and get someone in trouble and be seen as a snitch but if that shite had been videoed it would have gone viral. He would definitely been fired and maybe been prosecuted. I kind of need to cover my own arse too. What if it gets out and then I am questioned about why I never told the HC? Maybe I will just talk to him today and tell him he might want to check that behavior in the future and that while I will let it slide this one time....I will have no other choice but to report it to the HC next time to cover everyone's arse.