American Football NCAA Rule 2-8-1 through 3

Article 1 – Fair Catch

a. A fair catch of a scrimmage kick is a catch beyond the neutral zone by a Team B player who has made a valid signal during a scrimmage kick that is untouched beyond the neutral zone.
b. A fair catch of a free kick is a catch by a Team B player who has made a valid signal during an untouched free kick.
c. A valid or invalid fair catch signal deprives the receiving team of the opportunity to advance the ball. The ball is declared dead at the spot of the catch or recovery. If the catch precedes the signal, the ball is dead when the signal is first given.
d. If the receiver shades their eyes from the sun without waving their hand(s), the ball is live and may be advanced.

Article 2 – Valid Signal

A valid signal is a signal given by a player of Team B who has obviously signaled their intention by extending one hand only clearly above their head and waving that hand from side to side of their body more than once.

Article 3 – Invalid Signal

An invalid signal is any waving signal by a player of Team B:
a. That does not meet the requirements of Article 2 (above); or
b. That is given after a scrimmage kick is caught beyond the neutral zone, strikes the ground or touches another player beyond the neutral zone (A.R. 6-5-3-III-V); or
c. That is given after a free kick is caught, strikes the ground or touches another player. [Exception: Rule 6-4-1-f]