Science Fair Project Encyclopedia
Extra time is only played if the game is required to have a clear winner, e.g. in a knockout tournament where only one team can advance to the next stage. In professional play extra time is almost always an extra 30 minutes, made up of two 15-minute periods.
If such a game is still tied after extra time it is usually decided by kicks from the penalty mark (commonly called a penalty shoot-out).
Extra time should not be confused with the time added on to each period by the referee in allowance for time lost through substitutions, timewasting, injuries, etc (such time being part of the period concerned).
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