It's amazing you can target Krug on that play when there were much more egregious breakdowns.
Its not just this play or this breakdown, its been two season worth of breakdowns and losing his matchup more than any defender on the team.
Follow stats apply to players who played at least 40 games during the regular season:
2018 playoffs:
Krug: 7th (worst on team among defenders)
2018 regular season:
Krug: 6th (worst on team among defenders with at least 40 games played)
2017 regular season:
Krug: Worst among Bruins defenders to play at least 40 games
Now lets check plus/minus:
2017 regular season:
Krug: -10 worst on team among defenders to play at least 40 games)
2018 regular season:
Krug: 0 (worst on team among defenders to play at least 40 games)
2018 playoffs:
Krug: Worst among defenders on the team.
This isnt a new thing for Krug. 150 games worth of trend in the same direction. More than enough of a sample size to draw conclusions to his terrible defensive play.