originating from the game of tag, where several parties (generaly male) flick each others testicles with their hands without intent to injure, but to send an unpleasant twinge to the other person's testicles.

A back handed smack to the scrotum of another man (also known as "sacking"). Often resulting in a "tag war" where two men will bag tag each other multiple times in an effort to take take one's adversary by surprise. A tag war can be ended with a sacking/tagging truss.

To tag a male's crotch in a photo on facebook

When someone hits someone else in the bag and yells bag tag.Also look up sack attack

a family oreinted game played by "tagging" ones sack rather hard