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, the team which scores more away goals qualifies for the next stage. If this procedure does not produce a result, i.e. if both teams score the same number of goals at home and away, two 15-minute periods of extra time are played at the end of the second leg. If both teams score the same number of goals during extra time, away goals count double (i.e. the visiting team qualifies for the next stage). If no goals are scored during extra time, kicks from the penalty mark determine 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.
Kicks from the penalty mark are taken in accordance with the procedure laid down in the IFAB Laws of the Game.
The referee decides which goal will be used for the kicks:
If either goal could be used for the kicks, then, in the presence of the two captains, the referee tosses a coin to decide which goal will be used.
For reasons of safety/security, state of the field of play, lighting or other similar reasons, the referee may decide which goal will be used without tossing a coin. Such decisions are final.
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 kicks from the penalty mark.