Offside has a unique implementation in field lacrosse. Instituted with rule changes in 1921, it limits the number of players that are allowed on either side of the midfield line. Offside occurs when there are fewer than three players on the offensive side of the midfield line or when there are fewer than four players on the defensive half of the midfield line (note: if players are exiting through the special-substitution area, it is not to be determined an offside violation).