The United States’ Timothy Weah had a goal disallowed shortly before half-time after the referee signaled him offside.
You may be confused about what offside is and what it is, so here’s an explanation:
First, only the team that has possession of the ball in the opposing half is considered offside.
Suppose a player on Team A is playing with the ball. A teammate of that player is offside if his teammates – including head, arms, body and feet – are in front of the ball and no at least two Team B players (including the goalkeeper) are in or in front of them during the game up.
It’s a bit like camping conveniently on the goalposts, waiting to catch the ball.
Even if the teammate does not pass the ball, their early positioning so close to the goal or the opposing goalkeeper can put them offside, colloquially known as “still interfering with the game”.
Timing is of the essence. Because when a teammate receives the ball while offside, they are free to overtake the B team players, approach the goal and score.
Exceptions to this rule are corner kicks, goal kicks and throw-ins.