As an isolated incident, what Kadri did was reckless and hot-headed.
This happens to be one of the very few hits like that where context makes a difference though. The officiating was an absolute joke, that game got way out of hand and the Bruins were cheap-shotting the Leafs at every turn with no intervention whatsoever from the officials. With Wingels coming in with a leading elbow on Marner, Kadri probably had enough of the garbage and decided to fight fire with fire. But yeah, suddenly the refs needed to intervene despite ignoring everything prior to it.
@Pookie, not once have I seen you bring up any of this context. You just continue being dishonest with your little tirade against Kadri. You're not here to have any reasonable discussion.