I’d like to know how the guy could tell the difference between someone banging his head against a metal wall vs. HAVING his head banged against a metal wall...
In an area that small it isn’t really that hard to distinguish. Someone doing the banging would be making physically exerting noises in the process. Sounds of a scuffle are fairly distinguishable and I doubt anyone will simply go limp and let themselves be smashed into walls. Even if they are after the lawsuit lottery. The body will simply react automatically to defend itself.