WR - false start vs. illegal motion vs. illegal shift

[Robert Goodman]

Originally Posted by stegenref

[Define "started moving"]

He started moving in that he leaned forward, then took a step, and crossed the line of scrimmage...he was heading out to either block or run a pattern.

If it was Fed rules you'd kill the play for encroachment. Otherwise unless it qualified as a false start (which it probably didn't), he can get back and reset a second before the snap, to avoid a foul for either encroachment or illegal motion (encroachment being the easier call) as the ball becomes live, which can lead to an enforcement or declination (or cancellation) of penalty.