The ability of defensemen to affect shot quality against does exist in the population, but it is so small that we will never be able to sensibly apply it to any player in particular. - Vic Ferrari
Conceptually, that sentence might be tough to accept - "good" defensemen are good defensemen because they keep opposing skaters to the outside, clear pucks and bodies in front of the net, don't turn the puck over in dangerous spots, and so on; "bad" defensemen are bad defensemen because they allow high-quality scoring chances at an alarming rate. It would stand to reason, then, that goalies have higher save percentages behind the "good" defensemen and lower percentages against the "bad," right?
Not so fast. To begin with, match-ups have to be considered. Ferrari elaborates on the statement above:
[A] paradox is created, the type of defensemen who are helping the goalie save percentage a bit (presumably because they make fewer mistakes of the spectacularly bad variety) are, as a group, seeing slightly worse save percentages behind them, because they are the guys the coaches are leaning on to play tougher opposition. And the guys who have talent but are guilty of the occasional egregious error ... as a group, they do a whisker better than average by 5v5 save percentage score. This is presumably because their coaches have the good sense not to play them much against Malkin, Kovalchuk and Heatley types.
The result is that a defenseman's save percentage (that is, the team's save percentage at even strength with that defenseman on the ice) isn't a terribly good proxy for ability at all. For example, Nicklas Lidstrom was fourth among Detroit rearguards in save percentage this past season, Shea Weber was second from the bottom for Nashville and Zdeno Chara was third in Boston. All three of those defensemen were all finalists for the Norris trophy.
That said, a defenseman who is out-performing his teammates in this metric - regardless of the competition he's facing - is either getting very lucky or doing everything that's being asked of him... or a combination of the two. Enter John Erskine, who, in each of the past four seasons (i.e. the Bruce Boudreau era), has had a higher-than-team-average DSV%, but has also routinely faced weak competition (in 2010-11, for example, Erskine had the lowest Quality of Competition of any Caps defenseman who played at least ten games). Erskine played well against poor competition - he's a player whose been put in a position in which he can succeed, and he's succeeded.
But what about the rest of Erskine's teammates? To begin with, throwing all the defensemen who have suited up for the Caps over the past four seasons wouldn't be of much value - the team's even-strength save percentage in 2007-08 was .911; in 2010-11 it was .925. So, while it's a bit crude, we'll look at the difference above or below the team save percentage when comparing the blueliners. And to incorporate the "match-ups" component, we'll plot each player's SV% delta and quality of competition (QualComp) for that season. The results are after the jump.
Click to enlarge; Note some seasons with relatively few games played don't appear on this chart; Note also that the x-axis runs from -0.075 to 0.075 and the y-axis runs from -0.030 to 0.030
There's a lot to digest there, but here are a few key points:
- If you asked most Caps fans which were the best five defensemen seasons of the Boudreau era, Jeff Schultz in 2009-10 and John Carlson and Karl Alzner in 2010-11 certainly would make the list, so it's not surprising to see them in the upper right quadrant. Would those other two have made the list, though?
- Mike Green underperformed the team's save percentage in the two years that he faced tougher competition and outperformed save percentage when he faced softer competition. That might generally be considered "as expected," and is an argument to use he and Roman Hamrlik as a second pairing against other than opponents' top lines.
- How about Erskine? While outperforming save percentage when facing inferior competition might be expected, the degree to which he did so in 2008-09 and 2009-10 is awfully impressive... and/or lucky.
- Carlson and Alzner were unreal last season, but as is the case with all of these numbers, it's hard to divorce "great defensive performance" from "fortunate goaltending performances while on ice." Then again, Alzner was on the ice for more soft goals than any Cap blueliner. Still, don't be surprised to see some regression (in numbers, at least) from the duo in 2011-12, despite their respective developments.
- Schultz has been around average for the three seasons other than his monster 2009-10, which probably runs contrary to the perceptions of both his biggest detractors and supporters. Could it be that the most polarizing of Caps defensemen is actually the most vanilla?
- Tyler Sloan faced weak competition and underperformed the team's save percentage (though not drastically) in each of his three seasons in Washington. That, in and of itself, doesn't make him a bad defenseman; his skillset does.
- In two seasons with very small sample sizes, Sean Collins greatly outperformed the team's save percentage (by .011 in 2008-09 against weak competition and by a whopping .025 this past season against tough competition). He's might be alright as the eighth or ninth defenseman on the depth chart.
What we see above is pretty much in line with the general consensus on defensemen's ability to impact save percentage - it exists, but it's awfully hard to quantify and especially to predict, given all of the moving parts (see Poti, Tom). But it's interesting nonetheless and provides plenty of food for thought, especially as we look towards next season and play armchair head coach with the D-corps.