I can imagine some cases where it could be better for a helmet to come off than to stay on, which might allow more force to be applied, thus injuring the player’s neck.
But my only personal experience with helmets is with motorcycle helmets, which are not supposed to come off under any circumstances, so it always seems odd to me that helmets come off so often.
They don’t come off very easily. Once a game at most, and usually it’s because the dehelmetee didn’t buckle his chin strap properly.
I don’t know, it sure seems to happen a lot more than it used to – seems like 2-3 times a game on average (subjective impression, could well be wrong).
No, they shouldn’t. Generally, when they do, it’s because they’re not being worn safely. Players very often don’t use the chinstrap as securely as it’s intended to be used. For instance, some straps are four-pointed, meaning there are two snaps on each side of the helmet. Players frequently fasten only one on each side. See here, for instance. (I think it’s kind of funny that I found an example on the first guy I looked at just by picking a Miami guy). The chin strap is the only part of the helmet keeping it down on your head unless you’ve got it very tightly inflated to fit your cranium (another element that is sometimes overlooked for comfort or convenience’s sake), so if you don’t fasten the strap securely and take a good pop, off goes the helmet.
Edited to add - by contrast,this is what a properly snapped helmet of the same type looks like. A guy who takes enough licks over the course of a game to know the difference is a lot more likely to fasten it correctly.
It’s kind of like asking “should downhill ski’s come off easily?”, yes mid play your melon is vulnerable if the helmet gets pulled off, but I cringe every time I see an intentional facemask and the helmet doesn’t come off.