Bunting approached Mikhail Sergachev, and the two began trading blows because Bunting realized that his top player, Marner, couldn't continue to be treated that way. Another official began to push a Maple Leafs forward while the first referee proceeded to intervene to break up the fight and determine who would be sent to the penalty box.
You really don't see that too frequently, so you have to wonder if the NHL will penalize the referee or if an apology will be issued. This is not the first time this referee and the Leafs have been involved in an altercation; in 2016, the referee, who was a former player, delivered a vicious blow to a Leaf.