What Is the Offside Rule in Football?

The offside rule in football (soccer) is designed to prevent players from gaining an unfair advantage by positioning themselves too close to the opponent’s goal. A player is considered offside if, at the moment the ball is passed to them, they are closer to the opponent’s goal line than both the ball and the second-to-last defender (the last outfield defender, with the last defender usually being the goalkeeper) are and they are actively involved in play.

The offside rule includes several important nuances. Simply being in an offside position, for example, is not an offense—a player is penalized only if they receive the ball or interfere with play from that position. A player is considered onside if they are level with the second-to-last defender, and only parts of the body that can legally score a goal are considered in the decision. Offside is judged at the moment the ball is played, not when it is received, and situations can change depending on whether a defender deliberately plays the ball or it deflects off them. In addition, the rule does not apply when a player is in their own half of the field or receives the ball from a throw-in, corner kick, or goal kick.

The modern offside rule in football is derived from rules first introduced in the mid-19th century, with an early version appearing in the Cambridge Rules of 1848. At that time the rule was stricter: Players were considered offside unless they had several opponents between themselves and the goal. The rule was formalized by the Football Association, the ruling body for English football, in the 1860s, and it has been modified multiple times since to encourage more attacking play.

Today the precision of offside decisions can be augmented with the use of technologies such as video assistant referee (VAR) with semi-automated offside technology (SAOT), which help reduce controversial calls. These innovations aim to prevent incidents such as the infamous 1981 “lost goal,” when Kevin Keegan on Southampton FC executed a flawless bicycle kick against Manchester United, only to have the goal denied after officials judged teammate David Armstrong, who was questionably involved in the play, offside.