Can be read here.
The Illegal Player penalty called on Flint was because they sent a player off the bench instead of sending someone to the penalty box to finish a major penalty. It could not be called until there is a stopage of play. It was pointed out to the Ref and he made the call. The Boarding Major required a player to be in the box and come out of the box at the end of the penalty. It is Flints responsabilty to put someone in the box. I hope that helps your readers understand that call.
It sure helps me dschebig. I was at a lost when they made that call, and no one around me knew why it was called. Most fans around me thought that Flint had try to skate someone that had been a scratch. So thank you for clearing that up!