The team that holds the lead seeks to use as much time as possible, typically favoring run plays over pass plays. A drive that scores no points may nevertheless benefit the team by taking time off the clock. The team that is trailing seeks to conserve time, such as by passing (because an incomplete pass halts the clock) or by running toward the sidelines (because taking the ball out of bounds also stops the clock). If the defense is trailing, it can only control the clock by expending its time-outs. It may do so to ensure that there is adequate time left on the clock in case the team regains possession.
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. (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 within the last two minutes of the first half or the last five minutes of the second (or within the last two minutes of either half in college football).
- 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. The team loses no yardage by doing so, only the down, and gains the benefit of the stopped clock.)
- 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.
- "Digest of Rules: Timing". National Football League. Retrieved 13 January 2014.