It looks like the league is taking issue with that hit David Backes threw on Frans Nielsen after all.
Boston’s David Backes will have a hearing today for interference on Detroit’s Frans Nielsen.— NHL Player Safety (@NHLPlayerSafety) March 7, 2018
This appears to be a phone hearing, meaning five games or under.
My guess would be either a single game or a fine.
The interesting thing is that the league considers this worth punishment, but didn't think the same about the hit Nick Ritchie put on Backes several weeks back.
Here's last night's, in case you missed it.