The NFL got sued for an unaltered flag that hit a player in the eye. We can be sued for anything under the right circumstances.

Peace

There's no legal protection for an "unaltered" flag. Altering it in a reasonable manner should be fine.

I've been hit in the face with all sorts of crap -- baseballs, softballs, footballs, ice, even a BB or two. I'll take a long toss Honigs flag thrown from 5 feet away ANY time against any of this. This is sort of like stepping on someone's foot with cleated shoes: certain equipment is required and necessary and injuring someone with reasonable equipment accidentally is not going to be actionable in most states.