Ninjas Attack!

Karl and Alecia learned a game while living here in Utah.  It's called Ninja Attack.  Each player in turn must make one move, trying to hit the arm or hand of another player.  Other players can only move out of turn if they feel they are under attack.  Karl is pretty good at it.  They decided to teach Kayla and Patrick when they stopped in on their way to New Mexico for Christmas.  Karl got Alecia out, but her reflex to the hit made her arm fly in such a way that she slapped Karl on the face.  They laughed about it for a long time, but Karl never broke his concentration.