NCAA When does a scrimmage kick end

[chapmaja]

Referencing the Memphis punt return TD against Miss St.

Miss St punts, ball goes over return mans head, it saved from going into the endzone at the 2 yard line by a Miss St player, who bats is back to the 4 yard line. Ball is grabbed, then dropped by a Miss St player and rolls until it becomes motionless at 4 yard line (temporarily motionless, maybe a second at most). The official throws the beanbag and his hands are starting to signal stop the clock, but the whistle had not blown. Memphis player runs in, scoops up the ball and returns the punt for a 94 yard TD.

The announcers were talking about how Miss St stopped playing and it shouldn't have counted.

what I do know, is no matter what happened on the punt return, had he fumbled or loss possession, due to first touching by the kicking team, Memphis would retain possession of the ball.

The question is when, by rule, does the ball become dead on a scrimmage kick? I thought it was when the ball becomes motionless on the field of play. If I am correct in that thinking, how long does it need to be motionless?

No matter what, the fact the Miss St players just stood around might have been the second dumbest play I saw today (Colorado St not picking up a fumble was the dumbest).