After writing my post last night, I had a flashback to my freshmen Health class for PE majors in college (late 70's). We were actually told that we had a legal responsibility to monitor (ie--watch) the showers, as we were legally liable to:
a-prevent any dangerous play (including hazing) or injury that might appen
b-to monitor kids for physical signs of abuse such as bruise, scars, etc..

In the case of b, there had actually been PE teachers sued because they had not reported abuse that they should have seen if they had been properly monitoring students. In my own career, I have reported at least a few cases of abuse that no one else was clued into, based on scars on the back or legs. Two of these were kids who were burned with irons as children by their parents.

Interesting how our desire to prevent abuse may in fact be keeping us from spotting more of it.