Between game one of the season and March 3rd the Dallas Stars were a 51 percent Corsi team. A more concrete way to visualize this is that for every 100 shots attempted during a Stars game the Stars took 51 of them. 51 percent is a middle of the pack even strength team this season.
Since March 3rd the Stars are a 55 percent Corsi team. The Los Angeles Kings, leading the NHL currently, are at 54.8. To state the obvious for the dense among us: the Stars have been an elite team in March. March 3rd is a crucial date. The third coincides with the departure of veteran Trevor Daley from the lineup and the returns of both Patrik Nemeth and Tyler Seguin.
The Stars continued to score without Seguin so we'll focus on the defensive shift. This isn't to say that Seguin isn't important - far from it. However, the biggest difference we've seen lately has been an improved defense. Odd man rushes are less frequent. Defensive breakdowns have happened, but they occur with less frequency. The goals against are down. Kari Lehtonen's save percentage is up. How much of this has to do with Daley?
The short answer here is that we don't really know. It could be a coincidence. It could be a shift in strategy. It could just simply be the young kids getting better. Really, it could be all of these things, but it would be disingenuous to ignore the available data that suggests the Stars need something different from Daley.
I've mentioned this before, but it bears repeating here again. When Daley is on the ice something bad happens. For lack of a better term we'll officially dub it the Trevor Daley effect. This season when he has been on the ice every player has had mildly to significantly worse Corsi percentages compared to when Daley isn't on the ice with them.
The specific number of percentage points each player dropped isn't as significant the fact that they're all in the red with Daley compared to without him except Travis Moen. This isn't a case off a few outliers in a larger set of data. This is an entire team, one filled with high quality players, performing significantly better without Daley on the ice.
An argument could be made that Daley faces more difficult minutes than his teammates, but it doesn't hold up. He's 5th on the Stars in Quality of Competition and he actually gets 52.7% of his zone starts in the offensive zone. The main argument in favor of him facing difficult minutes is the Quality of Competition, but how much of an impact does that really make on the results? Eric Tulsky explains:
These competition metrics provide valuable insight into what a coach thinks of a player and how he tries to use them, but in practice they do not show differences large enough to have significant impact on the player's results.
A perfectly natural instinct would be to ignore the data, but the decision makers within the Stars really shouldn't. It's natural because Daley does look the part. He looks like he plays defense well. He can skate. He has 16 goals. He's physical. He just looks like an NHL defenseman. There is a lot to be said for that, but not enough to invalidate such substantial data.
The most obvious example that comes to mind to explain the significance of observation vs data is student test data. When student information comes back that doesn't meet the expectations you had the first response is "why" or "how do I fix this". Intelligent students can fail tests easily if they have a previously unidentified deficiency. Some have test anxiety, other have difficulty reading, and some have trouble at home. The point is that sometimes things happen that lead to troubling data. This doesn't invalidate the data, but it does mean that there is an issue somewhere which needs to be fixed.
It would be hard to pinpoint exactly what is causing it to happen, but whatever is causing it to happen is impacting Daley at both ends of the rink. I pulled some information from War-On-Ice to illustrate the point a little clearer. CF60 is Corsi attempts for per 60 minutes, CA60 is Corsi attempts against per 60, and the final column is the difference between the two.
What we can see pretty clearly is that Daley is significantly behind the pack. For every 60 minutes of play the Stars are giving up ten more shot attempts at net with Daley on the ice than they are attempting. Both the Stars lowest offensive output and worst defensive output are with Daley on the ice. Further complicating the issue is that one of Nemeth, Jamie Oleksiak, or Jyrki Jokipakka will sit when Daley returns. Based on results from the entire season that swap will cost the Stars anywhere from seven to 15 shot attempts against every 60 minutes.
Fixing the issue with Daley at even strength isn't necessarily going to hurt his offensive production either. He isn't going to continue shooting 14%. The goal total is unreasonably high compared to what should be expected from a consistent 6% shooter, but he produces on the power play so he will continue to be able to be a valuable offensive lpayer.
The Stars need to get more productive even strength play out of Daley. He could provide the Stars with value going forward, but if the aforementioned trends continue with all of the surplus young defensemen Jim Nill has stockpiled the Stars might have to consider moving on from Daley in the offseason to take the next step.