The free lap rule is one that can be confusing. The use of the rule is dependent upon the time your mishap occurs during the race.
Be familiar with these points and how to work with race officials if you are ever faced with a mishap during a crit. Wondering what to do when your heart rate is still elevated and you’re anxious to latch back on isn’t the best scenario for clear thought. This is a chance to get it into your head before it happens on the bike.
This is the rule as stated in the USA Cycling 2014 Rulebook:
3D5. Free Lap Rule. Riders shall normally cover the distance of the race regardless of mishaps and must make up any distance lost on their own ability unless a free lap is granted for mishaps. Unless the official race announcement states that no free laps will be allowed, one free lap may be granted for each mishap subject to the following rules. On courses shorter than 1 km, two free laps may be allowed for a given mishap.
(a) Bicycle inspection and repairs must be made in an official repair pit. If announced in advance by the Chief Referee, riders are permitted to cut the course to get to a pit, but only while the Free Lap Rule is in effect. There should be repair pits at intervals of 1 km around the course.
(b) There must be a referee stationed in each repair pit to determine if the mishap was a legitimate one and if the rider is entitled to a free lap.
(c) A rider who is granted a free lap must return to the race in the position held at the time of the mishap. A rider who was in a group shall return at the rear of the same group the next time around. A rider returning to the race after a free lap shall be ineligible for sprint prizes for one lap thereafter.
(d) A rider granted a free lap must re-enter the race before the final 8km of the race; after that point in the race a rider in the pit is losing ground on the field.