PSU utilises Julius as part of their coverage, not just the safety. He should be blocked/hit every kick. I didn't see the entirety of that play, just the replay showing the hit. If after the whistle then it is a dirty play and the ejection was warranted. If the play is still in progress i.e. before the whistle, then he is fair game as he is still running towards the play at the time of the hit. He knows if the ball is downed and can stop pursuing. The blocker cannot see that so should continue to block until the whistle blows.