The infraction came midway through the third period with the Bruins up 4-1. Kadri was assessed a five-minute major and game misconduct.
The NHL, in its player safety video, deemed the hit "forceful and illegal" and stated that it was "delivered on a defenseless opponent for the purpose of retribution and message-sending."
"I certainly wasn't trying to hit him while he was down like that. I was already committed to the hit. If he's still standing up, there isn't anything wrong on that, but he fell," Kadri said Thursday night, according to ESPN.com's Greg Wyshynski.
"Initially I thought he just made contact with [Mitch Marner's] head to start and I didn't see a call there," Kadri added. "He was turning up the wall, so I was committed to the hit. He ended up falling. It happened pretty quick, and I think he was reaching for the puck. I don't think I stuck my leg out or my arm out, or whatever the case is, but it's in the hands of the NHL at this point."
Game 2 between the Bruins and Maple Leafs is scheduled for 8 p.m. ET Saturday night at TD Garden.