What are SEC rules regarding fans keeping footballs thrown into stands?

by mary sparks
(hot springs ar 71913)

my grandson, age 11, caught a football that was thrown by a new mexico player sat. nite in little rock ,, ar. they were playing the arkansas razorbacks.

he was told by an officer( not sure which division ie. state or local) that he had to turn the ball back, which he did.

what are the rules about allowing a fan to keep the ball when it is off the field?