Rules for the game clock
Upon kickoff, the clock is started when a member of the receiving team touches the ball, or, if the member of the receiving team touches the ball in their end zone, carries the ball out of the end zone. The clock is stopped when that player is tackled or goes out of bounds. However, in the NFL the clock runs when a player goes out of bounds unless it's the final two minutes of the first half or final five minutes of the second half. (The clock never starts if the receiving team downs the ball in their own end zone for a touchback.) The clock is then restarted when the offense snaps the ball for their first play and continues to run unless one of the following occurs:
- A player carrying the ball goes out of bounds.
- A forward pass is ruled incomplete. (Included in this is the rule whereby the quarterback can "spike" the ball near himself without being called for intentional grounding.)
- Either team calls for a time-out or an official calls for a time-out, perhaps because a player is injured or there is a penalty on the play. Officials will restart the clock after an official time-out, but not a team time-out, has concluded unless another of the conditions applies.
- A player from either team scores. Additionally, the clock does not run during or after a conversion attempt in the NFL or NCAA college football.
- Possession of the football is transferred between teams for any reason.
- In college football, the clock is briefly stopped when a team earns a first down to allow the chain crew to reposition themselves. The NFL has no such stoppage.
- The clock runs out. If this happens during a play, the current play continues until the ball is dead.
Each team is given three time-outs per half which they can use to stop the clock from running after a play.
A team on offense that has the higher score seeks to use as much time as possible. A drive that scores no points may nevertheless benefit the team by taking time off the clock. The team may:
- Favor run plays over pass plays.
- Use the center of the field rather than the sidelines to avoid going out of bounds and stopping the clock.
- Delay the start of each play until the play clock approaches 0.
The team may use counterintuitive game plans, such as declining to score or allowing the opponents to score, to accelerate the end of the game.
A team on offense that has the lower score seeks to conserve time. The team may:
- Use a no-huddle offense; forego detailed design of a play and instead signal and initiate a play quickly.
- Have the quarterback "spike" the ball, sacrificing a down to stop the clock.
- Use a passing play (because an incomplete pass halts the clock) or a run play toward the sidelines (because taking the ball out of bounds also stops the clock).
- If a play ends such that the game clock continues running, use a time-out.
A team on defense has little control over the pace of the game. It may expend its time-outs to ensure that there is adequate time left on the clock, in case the team regains possession.