Confused by the 40-second play clock?

How the play clock works:

The offense has 40 seconds to snap the ball after the previous play ends. The ball is ready for play when an official spots the ball and steps away to his position. The referee does not give a ready for play signal and does not wait for the chains to get set after a first down to start the game clock. The 40-second clock should still start at the end of the previous play if there was a first down.

A 25-second clock is used after an administrative stoppage. These are administrative stoppages:

• Penalties
• Timeouts
• Injury/Helmet off
• Measurement
• Change of Possession
• Touchdown
• Try/FG/Safety/Kickoff
• Start of overtime

If the 40-second count is interrupted because there is an appreciable delay in spotting the ball or for reasons beyond the control of the officials, the referee shall stop the game clock and signal to the back judge (both palms open in an over-the-head pumping motion) that the play clock should be re-set at 25 seconds and started when the ready-for-play signal is given.

Event *	Play Clock Starts at	Game Clock Starts on	Covering Official’s Signal		Referee’s Signal
Dead ball inbounds	40	Running	S7		None
Dead ball out of bounds	40	Snap	S3		None
Incomplete pass	40	Snap	S10		None
Team A awarded 1st down	40	Signal	S3		S2
Penalty administration	25	Ready	S3		S2
Charged team timeout	25	Snap	S3		S1
Injury/Helmet off	25	Ready	S3		S2
Measurement	25	Ready	S3		S2
Double Change of possession-  Team A snaps	40	Ready	S7		S2
Change of possession- Team B snaps	25	Snap	S3		S1
Touchdown	25	N/A	S5		S1
Try, FG, Safety	25	Varies	Varies		S1
Start of each period	25	Snap	N/A		S1
Legal kick	25	Snap	S3		S1
Start of an overtime period	25	N/A	N/A		S1
Other administrative stoppage	25	Ready	S3		S2

Position Mechanics 

Wings

The play clock starts as soon as the play ends and the ball is dead. On in-bounds plays, the covering official will raise his arm straight up for two seconds to indicate the 40-second play clock should start. On out-of-bounds plays, wave the clock dead just as you always have. You’re still signaling to the clock operator as you always have.

Back Judge

This rule gives you something to do back there. Simply, start the 40-second play clock when the previous play ends. At 10 seconds left, raise your arm until five seconds and start chopping.

Referee

If the ball is not spotted with approximately 20 seconds remaining on the play clock, re-set the play clock to 25-seconds. The only thing you actually need to worry about is not blowing your “ready” whistle on every play. You’ll still blow for resuming plays after administrative stoppages, but that’s all. Also, don’t wait for the chains to get set to start the game clock. You’re still signaling to the clock operator as you always have.