Of course, the idea of playing Marner as a defenseman is primarily to add weight to his team's offense, to try to score a goal in a critical moment.
However, playing as a back, it is possible that the situation requires defense and that is exactly what happened yesterday, when forward Nico Hischier came into the Toronto zone with the puck and challenged him one-on-one.
Not only was Marner unable to stop it, but the Devils' forward even took himself out of the game completely, finding himself alone in front of the goalie. Let's just say that Hischier gave him a real cup of coffee.