For matches played under the knockout system, if the two teams involved in a tie score the same number of goals over the two legs, two 15-minute periods of extra time are played at the end of the second leg. The team which scores more goals during extra time qualifies for the next stage. If both teams score the same number of goals or no goals are scored during extra time, a penalty shoot-out determines which team qualifies for the next stage.
If extra time is required, there is a five-minute break between the end of normal time and the start of extra time. As a rule, the players remain on the field of play during this five-minute break, at the discretion of the referee.
Penalties are taken in accordance with the procedure laid down in the IFAB Laws of the Game.
To ensure that the procedure is strictly observed, the referee is assisted by his team, who also note down the numbers of the players on each team who have taken penalties.