Why don't football refs (College, NFL, High School) where helmets? Hockey
refs do.

I see NFL refs digging in piles of players, trying to break up fights between
opposing sides, and otherwise in close proximity to very large men moving
erratically and with considerable force.

Umpires and Back Judges are directly in the field of play and have been known
to be hit by receivers and defenders running routes.

They need not where a helmet the size of those worn by players, but it
certainly seems like having some head protection out there would be a good
idea.

Using a cap to mark the ball or call a foul could be done some other way, so that doesn't seem to be a good reason to avoid a helmet.

I bet if one researched it, you'd find that refs have been hurt in various ways - and probably knocked in the head a time or two.

The NFL now has PSAs to warn of the dangers of head injuries. So they are thinking a lot about it. But what about the refs?