WHEN DOES A 10-SECOND RUNOFF OCCUR?
When there is a 10-second runoff, the clock starts on the referee’s signal. A 10-second runoff occurs when a team commits any of these acts after the two-minute warning with the clock running:

An offensive foul that prevents the snap (e.g., false start)
Intentional grounding
Illegal forward pass thrown from beyond the line of scrimmage
Throwing a backward pass out of bounds
Spiking or throwing the ball in the field of play after the down ends (except after a touchdown)
Any other intentional foul that causes the clock to stop
There is a 10-second runoff if a replay review of a play after the two-minute warning results in the on-field ruling being reversed and the correct ruling would not have stopped the clock.

This runoff only applies to the offense. The defense always has the option to decline the 10-second runoff and have the yardage penalty enforced, but if the yardage penalty is declined, the 10-second runoff is also declined.