off·side\ˈȯf-ˈsīd\
adverb or adjective
sports : in a position in a game (such as football or hockey) on the opponent's part of the field where you are not allowed to be : not onside
: on the right side
Full Definition
: illegally in advance of the ball or puck
First use: 1867
原汁原味学英语：offside!