Law 7 requires the referee to make allowance in either period for "all time lost through:
- assessment of injury to players
- removal of injured players from the field of play for treatment
- wasting time
- any other cause"
Law 7 notes that the "allowance for time lost is at the discretion of the referee." More recently, in Memorandum 2001, USSF reported FIFA's position that, although the safety of players must be the main priority, referees were "instructed to add the full amount of time lost for reasons relating to injuries."
Most stoppages of play are ordinary elements of the game and "time lost" is a much more restricted concept than "time not played." The Laws of the Game encourage a match management approach by the referee that keeps the game moving with as few stoppages of play as possible and a minimum amount of delay in all restarts.
Referees must provide players with full adjustments of time for delays that are longer than what is minimally needed for the purpose of the restart. In general, most ordinary restarts can be accomplished quickly, regardless of the reason (substitution, goal celebration, disciplinary action, assessment of injury, and so forth). In such cases, the referee is not expected to consider the time as "lost."
Where delays are excessive, however, the referee is obliged to take their length fully into account in timing each half. Such decisions must always be made in accordance with the referee’s feeling for the spirit of the game.