[adjective], [adverb] [not gradable] - (in football and some other sports) in a position where you are allowed to kick, throw or receive the ball or puck In football, a player is onside if there is a member of the opposing team between the player and the opposing team's goal when a member of the player's own team kicks the ball.Compare offside (NOT ALLOWED).
ONSIDE
Meaning of ONSIDE in English
Cambridge English vocab. Кембриджский английский словарь. 2012