Don't remember if the NCAA has this rule, and don't have time to check right now, but...
In NFHS, this is a foul because the player is not within the numbers at any point after the ready-for-play. We can see the white hat clearly and he never blows it in while he is on screen, and then the WR is at the sideline.
Honestly, that would be the "friendly" call, though, because that's only a 5-yard penalty - I see this as a pretend substitution, which would be 15.