I disagree, since you can have one player in motion going backwards or parallel to the line of scrimmage, I didn't see anyone else moving at the time of the snap. I do agree he probably was moving backwards expecting a earlier snap, but since you can have one in motion (backwards or parallel to the line) I do not have a flag. Maybe you could argue the running back had moved and was not set for a full second and then if that was you interpretation then you could flag for illegal motion. I would do a little preventative officiating after the play and let the QB know had anyone been in motion when he started moving back he would have been flagged.