In the last couple of weeks, I've noticed a distinct lack of gleeful comments posted by Bruce giving New Jersey's goalie stats since Martin Brodeur went down. I decided to look into it myself to see just how New Jersey's replacement goalies are holding up.
Scott Clemmensen: 7-3-0, 2.19, .926
Kevin Weekes: 2-3-0, 2.86, .903
Backups Combined: 9-6-0, 2.42, .918
Martin Brodeur: 6-2-2, 2.16, .916
So far I'd say they are doing pretty well. It is a very small sample size to be sure, and it is certainly much too early to discount the possibility that Scott Clemmensen may just be playing way over his head for a couple of weeks. However, I am just as interested in the number and type of shots Brodeur's replacements are facing, rather than simply whether they are stopping them or not. I cruised over to Hockey Numbers to see what his shot-quality calculations are telling us about New Jersey's goalies. SQN% is shot-quality neutral save percentage, and SQI is shot quality index (1.00 is average, below 1.00 means a team allows easier than average shots).
Brodeur: .914 SQN%, 0.98 SQI, 25.7 SA/60
Clemmensen: .918 SQN%, 0.90 SQI, 29.5 SA/60
Weekes: .892 SQN%, 0.90 SQI, 29.6 SA/60
Clemmensen and Weekes are very similar in their underlying numbers, facing almost identical shot quality and quantity. The difference is that Clemmensen is making more saves.
What really stands out, however, is that Brodeur has faced 4 fewer shots per game than his backups goalies have. Is this finally evidence of his soft goaltending skills as a third defenceman out on the ice, or are there other factors at play? In hockey, there are pretty much always other factors at play. If we look at the shot quality numbers, Clemmsen and Weekes have faced shots that were estimated as being 10% easier than average. Brodeur's shots were only 2% easier than average. This means that while New Jersey has allowed more shots without Brodeur in net, the extra shots faced have been apparently much easier to stop. If the primary reason for the difference was Brodeur's impact on puck possession, I'm not sure that we would expect to see a difference in shot quality.
Obviously we need to track shots and shot quality over a larger number of games to see if these differences are fluke or reality (and there are a number of factors that make shot quality less than perfectly reliable, such as reporting bias, failure to consider shot angle, etc.), but there are two possible explanations that do come to mind that could explain these results (maybe New Jersey fans can weigh in if either of them seems reasonable). The numbers suggest that either opposing teams are shooting from everywhere to test Clemmensen and Weekes, or New Jersey has changed its defensive style of play to protect their goalies which has resulted in allowing a higher number of lower quality shots.
We can try to quantify the goal prevention effect from the difference in shots allowed, by estimating the expected goals against by an average goalie facing Brodeur's shot distribution and then comparing that to his backups. The league average so far is .907, so let's go with that as our baseline number. We can adjust that for the shot quality for each goalie, and then multiply that by number of shots actually faced to get an expected GAA.
Here are the results:
Through an expected goals approach, Brodeur's 4 fewer shots per game translate into a GAA effect of -0.15 goals per game. If we want to try to express that gap in terms of save percentage, it would be the equivalent of +.005 in save percentage for a goalie with a league average save percentage facing league average shots. We don't know at this point whether Clemmensen and Weekes are better or worse than average in terms of shot prevention, so it isn't necessarily correct to attribute the entire gap to Brodeur.
I don't know the typical starter/backup split in terms of shot quality, especially in this type of situation where lightly regarded backups replace an All-Star. However, there is a very similar situation going on in Vancouver, so I'll bring that in as a point of comparison. Here is how Luongo has done compared to his replacements by all the same metrics as above (SQN% = shot-quality neutral save percentage, SQI=shot quality index, expGAA = expected GAA for a league average goalie facing the same shots):
Luongo: 2.17, .928, .930 SQN%, 30.2 SA, 1.03 SQI, 2.89 expGAA
Sanford: 2.85, .905, .897 SQN%, 30.0 SA, 0.92 SQI, 2.57 expGAA
Schneider: 2.80, .896, .878 SQN%, 26.9 SA, 0.85 SQI, 2.13 expGAA
Backups: 2.83, .902, .891 SQN%, 28.9 SA, 0.90 SQI, 2.41 expGAA
The combined shot quantity and quality for Luongo's backups is very similar to Brodeur's (same shot quality against and a difference of less than one shot against per game). Just like Brodeur, Luongo has apparently faced more difficult shots, but Luongo has also faced more of them (1.3 extra shots per game than his backups). Luongo's expected GAA is actually 0.48 goals above that of his backups because of these factors, yet his actual GAA is 0.66 lower. According to the numbers, Vancouver has been hurt a lot more by goalie injuries than New Jersey has.
What about evidence that Brodeur affects his teammates, or that his puckhandling contributes to his team's offence? I went to Time on Ice to check out the possession statistics while each goalie was in the game (using Behind the Net's numbers to estimate minutes played at 5 on 5):
Brodeur: +8.4 Shot Diff/60, +7.9 Corsi/60, +12.1 Fenwick/60
Backups: +1.8 Shot Diff/60, +4.9 Corsi/60, +5.4 Fenwick/60
Luongo: -2.6 Shot Diff/60, -3.4 Corsi/60, -4.7 Fenwick/60
Backups: -2.9 Shot Diff/60, -4.2 Corsi/60, -7.5 Fenwick/60
Both goalies have better outshooting results than their backups do. New Jersey is obviously a better outshooting team than Vancouver, but Brodeur outperforms his backups by a larger margin than Luongo. Vancouver blocks a similar ratio of shots no matter who their goalie is, while New Jersey's shot block to total shot attempts against rate is 3% higher with Clemmensen or Weekes in net than with Brodeur.
One factor at work with the possession stats could be that Luongo has been in the lead much more often than his backup goalies. That may have led to more shots against, since there is some evidence to suggest that trailing teams are likely to shoot more. Vancouver tends to reduce their offensive pressure when they are leading, focusing instead on preserving the lead. New Jersey likely usually uses a similar strategy, but New Jersey's backups have a better record than Vancouver's so this may not have affected them as much.
It's pretty early to conclude anything, but there are a few observations to be made. New Jersey is a good team, and both the shot quality numbers and Scott Clemmensen's stats suggest they are still a very good defensive team. Playing in New Jersey helps a goalie's statistics, of that there is little doubt. However, the interesting numbers are the ones that relate to Martin Brodeur's impact on his team's play beyond stopping pucks (e.g. shots against and puck possession stats), and that is certainly something to follow along with as the season goes on.