the.com/offside

means A rule in football (and similar sports) that stops an attacking player from being nearer the opponent's goal line than the second-last defender when the ball is played to them.

from Straightforward compound of 'off' and 'side' — being off (away from) your proper side or position on the field. The term grew out of 19th-century English football codes, where early rules were far stricter (players needed three defenders between them and the goal, not two) and the offside concept itself borrowed from older rugby and 'mob football' traditions that policed forward play to stop goal-hanging. The exact wording has been rewritten many times since, but the core idea — don't lurk behind the defense waiting for the ball — has stayed put.