FORGET the shots to the head. Yeah, they'll hurt and they're some of the worst bleeders you'll get.
Helmets are mandatory (IMO) for CQB to guard against impacts with obstacles or falling/tripping/collsions/etc.....protection from BB shots is a side benefit.
Aside from the "inconsequential" bangs and bumps...I've seen a half dozen instances that were, "Holy Crap...stop everything and see if the guy is ok". Most had helmets on thankfully.
The worst one was a guy falling a story onto a concrete floor...he was laid out and went to the hospital. Ask Mr. Shiney if a helmet is a good idea. Don't ask him if he remembers that fall...he might not.
A real Protec skateboard helmet is way better than a clone OpsCore BaseJump that'll disentegrate in a real impact, just when your brain needs the protection....