Morgan Rielly has an incredible knack for creating offence. At 5v5 he's 5th in the NHL in individual shot attempts among defencemen this year. He's also 39th in points-per-60-minutes at 5v5 among defencemen despite playing on the team with the 5th fewest 5v5 goals. At just 21 years old, Rielly is already among the NHL's most productive offensive defencemen.
However, there remain significant questions about his defensive game. So far in Rielly's young NHL career, the Leafs have allowed a fairly high volume of shots while he's been on the ice. We can contrast Rielly's results with those of Jake Gardiner, who is consistently among the best Leafs at limiting opposition opportunities. Here we're looking at shot attempts allowed relative to the rest of the team. A lower number is better (ie. fewer shots allowed).
| Player | Season | CA/60 Rel Tm |
| Rielly | 2015-16 | 5.1 |
| Gardiner | -4.8 | |
| Rielly | 2014-15 | 1.1 |
| Gardiner | -9.0 | |
| Rielly | 2013-14 | 1.6 |
| Gardiner | -8.7 |
(stats via Puckalytics)
The Hunwick Effect
One thing that's noticeable about Rielly's results is that they've gotten much worse this season. It's surprising that a player would have worse results at 21 years old than at 19 or 20, especially given that the team is receiving much better coaching now.
Many fans have suggested that Rielly's statistics this season are not a reflection of his own shortcomings, but those of his primary defensive partner - Matt Hunwick. The evidence does not seem to bear this out.
The Leafs allow 61.7 shot attempts per 60 minutes at 5v5 (known as CA/60) with Rielly and Hunwick both on the ice. When Rielly is on the ice but Hunwick is not, the Leafs allow 59.5 CA/60. The difference there is not very large, especially given that the sample sizes we're working with are not particularly large.
Something else we can look at is where the shots come from when Rielly is on the ice. If Rielly's statistics were primarily Hunwick's fault, we'd expect to see the bulk of the shot attempts coming from Hunwick's side of the ice. Rielly normally plays the right side, while Hunwick plays left.
So here's where shots come from with Rielly on-ice (a higher number means worse results relative to league average):
Shots are primarily coming from Rielly's side of the ice, not Hunwick's. In particular, the Leafs allow an exceptionally high volume of shots from in close on the right side when Morgan Rielly is on the ice.
We can look at what those numbers look like when Rielly's on the bench to get a sense of whether this problem is Rielly-specific:
As you can see, the other right-side defencemen for the Leafs are pretty good at limiting shots from in close, and the number of shot attempts from the low slot are also much lower when Rielly is on the bench.
That Age Thing
Many people admit that Morgan Rielly needs to work on the defensive side of his game, but will say that it's fine because he's only 21 years old and will inevitably get better as he gets older.
To test that theory, I used Hockey Reference to pull a list of all the recent defencemen with seasons comparable to Rielly when they were 21 years old. I wanted defenceman who played a lot of minutes and also scored a lot of points (so that no one can complain I'm looking at "defensive" defencemen). For the purposes of this post, "comparable" means at least 1200 minutes of ice time and at least 30 points. I pulled data from 2007-08 (the first season Corsi data became available) up until 2013-14, which resulted in a list of 13 players.
What I wanted to know was, do young players comparable to Rielly typically struggle to limit shot attempts?
| Player | Season | Age | GP | PTS | CA/60 Rel Tm |
| Erik Karlsson | 2011-12 | 21 | 81 | 78 | -4.5 |
| Alex Pietrangelo | 2010-11 | 21 | 79 | 43 | -4.3 |
| Drew Doughty | 2010-11 | 21 | 76 | 40 | -3.8 |
| Kris Letang | 2008-09 | 21 | 74 | 33 | -3.4 |
| P.K. Subban | 2010-11 | 21 | 77 | 38 | -3.3 |
| Erik Johnson | 2009-10 | 21 | 79 | 39 | -2.6 |
| John Carlson | 2010-11 | 21 | 82 | 37 | -1.9 |
| Marc-Edouard Vlasic | 2008-09 | 21 | 82 | 36 | -1.1 |
| Justin Faulk | 2013-14 | 21 | 76 | 32 | -0.5 |
| Michael Del Zotto | 2011-12 | 21 | 77 | 41 | -0.4 |
| Jake Gardiner | 2011-12 | 21 | 75 | 30 | 2.3 |
| Morgan Rielly | 2015-16 | 21 | 51 | 23 | 4.7 |
| Zach Bogosian | 2011-12 | 21 | 65 | 30 | 5.1 |
The answer to my question is "no." Only one player here, Zach Bogosian allowed more shot attempts relative to their team-mates. In fact, the players who've gone on to become stars (like Doughty), typically had very good defensive results, even this early in their careers. That holds true even for players like Karlsson, Subban, and Letang, who are not normally praised for the defensive side of their game (but perhaps should be).
The one piece of good news for Rielly is that team-mate Jake Gardiner's results were not great when he was 21 years old, but they've been outstanding in recent years. That said, Gardiner is the only player here who bucks the trend, so it does seem pretty rare.
Rielly, Revisited
In the end, I think we have to conclude that Rielly's defensive struggles are a legitimate cause for concern. The evidence does not support the theory that Hunwick is unfairly dragging him down, so Rielly needs to take the blame for his defensive results.
As to whether he can improve as he gets older, he obviously can, but the history of young offensive defencemen suggests that players who go on to become real stars during their peak years are much better defensively even at a young age. That suggests to me that we should think of Rielly as a highly skilled offensive player who will need to be sheltered defensively, and likely will throughout his career.
