Apologies if this has already been answered.
That has been a rule for a long time for obvious reasons. Hard to believe he nor anybody else on his staff did not know it or at least didn't feel the need to verify the rule before the deed. Even if they really didn't know ignorance is no excuse and by rule your team should have been penalized 15 and RN disqualified.
You only get ejected for excessive abuse of the rule. The rule was in place since McKnight signed with USC west years ago. He and a defensive player both wore number #4. I thought he was going both ways until the announcers explained two players could wear the same number as long gas one was on defense and the other offense.He would have to be painfully stupid to know that rule and then break it, putting two key players at risk of being thrown out. As for the rule itself, I could see where it might give a competitive advantage to the guilty team in some instances, but this wasn't one. Still, by rule both should've been tossed.
Lining a 6' 5" NT up at RB is sneaky.