It's a live ball foul, flagged at the snap (if they're still standing in the restricted area at that time) or during the play. Remember the three-tier penalty: Warning on 1st offense, 5-yards on 2nd, and 15-yards USC on head coach subsequent offenses. I was told the other day that a crew actually flagged this about 6 times during a scrimmage, just to teach the team a lesson. I have a feeling the first couple weeks might see some flags for this and then it'll subside.