The best way to understand it would be to watch the movie The Blood of Heroes.
But jugging isa game were two teams of five try to take the Dog skull and put it on the enemy stake. I have not actually seen a game with a real dog skull, most use a piece of fun noodle. Each team has a quick, a chain, and three enforcers. In amtgard the quick is equipped with a dagger, but in the movie the quick has no weapons, and i have seen non-amtgardian quicks play without a weapon. The quick is the only one who can handle the dogskull. The chain is the guardian of the quick. In amtgard the chain fights using two flails, outside of amtgard the chain uses a plastic chain with a large foam ball on the end. The enforcers fight the other enforcers, trying to keep them buisy so they do not go afdter the quick. In amtgard the enforcers either fight pole, sword&board or flourintine. I do not know if it is differnt in the other games of it. The game is played for three turns of one hundred stones, which are represented by hitting a shield with a sword.
Thats the basics of jugging, juggers are players of jugging.