XARM contains elements of arm wrestling, kickboxing and jiu jitsu. A fighter's waist is chained to a 28" by 16" table and his left hand his taped to his opponent's. Contestants have three one-minute bouts to pin their opponent's arm or pummel him into a coma--whichever happens first.
Here's footage of an XARM match. Notice how the fighters immediately eschew the whole arm-wrestling thing for the alternative tactic of smashing each other's solar plexuses.
Referees award points for clean hits, successful grapples and standard arm wrestling pins. Points are deducted for a "failure to fight aggressively," which is a sort of redundant rule--after all, a sissy defense is kind of impossible when you're handcuffed to the guy who wants to eat your aorta.
But you can hide under the table.
In sum, XARM is the modern update of an old-timey saloon brawl. It begins as a sportingly macho test of strength on a bar table and ends with a very large man giving you punch-induced renal failure. That being said, we'd hate to see which arm German pro arm-wrestler Matthias "Hellboy" Schlitte would choose to wrestle with.
That's a pile driver or a wrecking ball. Your choice.