USA’s Timothy Weah was denied a goal shortly before halftime because the referee flagged he was offside.
You might be confused as to what and how offside is defined, so here’s an explanation:
First of all, only the team with possession of the ball in its opponent’s half of the field can be offside.
Let’s say a player on Team A is attacking with the ball. If this player’s teammate — head, arms, body and feet included — is ahead of the ball and doesn’t have at least two of Team B’s players (including the goalkeeper) in line or in front of them when the ball is played, then this teammate is offside.
It’s kind of like conveniently camping out at the goal post, waiting to receive the ball.
Even if this teammate was not passed the ball, the fact that they were positioned this close to the goal or opposition goalkeeper ahead of time makes them offside, colloquially referred to as “still interfering with play.”
And timing is of the essence. Because when the teammate receives the ball while onside, they are then free to outrun Team B’s players, get close to the goal and score.
The exception to this rule is corner kicks, goal kicks and throw-ins.