January 20, 2011
Howe and Why
Rozsival's Revival

by Robert Vollman

Phoenix and New York swapped high-priced underachievers lately, as the Rangers dealt veteran Czech blueliner Michal Rozsival and his $5.0 million cap hit for Wojtek Wolski and his $3.8. Before you declare this trade a low-risk victory for the Rangers, Rozsival's performance deserves a closer look.

In 2008, Michal Rozsival was 29 when he was rewarded for leading Rangers defensemen in scoring three seasons in a row with a four-year, $20 million dollar contract. His scoring then took a gradual decline, until last season when he finished fourth among Rangers rearguards. However, there's more to the story than can be told by the simple box score statistics.

Now don't get us wrong, our own analysis of Rozsival's situation in Hockey Prospectus 2010-11 was both scathing and accurate. We referred to his contract being a "money pit" and "even less of a bargain" than Redden's, and rightfully took exception to his remarkably undisciplined play. There's no doubt we'd have declared the Rangers the winner of a trade even if they had received Wojtek the soldier bear instead of Wojtek Wolski.

Unfortunately, there's the small matter of the tremendous territorial advantage the Rangers enjoyed this season with Rozsival on the ice. Rozsival's Corsi is up by a whopping 10 attempted shots per 60 minutes this year despite a higher quality of competition and lower quality of linemates. Last season, the Rangers enjoyed virtually no apparent benefit in having Rozsival on the ice, and this year they were up over 10 shots, the best on the team.

We need an explanation! How much of Rozsival's improvement is a consequence of his own ability, and how much of it can be explained by other factors? While we don't intend to answer this question definitively, we should have enough information to determine if the Coyotes acquired the quality blueliner they need, or just another albatross.

League of Extraordinarily Improved Players

Taking a page out of the approach Tom Awad used in the Good Player Series, and Ben Wendorf's naming conventions, we'll address the sample size issue by compiling a larger group of this year's most improved players. The League of Extraordinarily Improved Players (LEIP) includes everyone who played at least 40 games in 2009-10 and 20 games so far in 2010-11, and who improved their even strength Relative Corsi (their on-ice Corsi minus the team's Corsi without them) by at least as much as Rozsival's 10.

At the moment, LEIP includes 52 players, including five Columbus Blue Jackets, four Chicago Blackhawks, and between one and three representatives from 21 of the league's 28 other teams.

Conceptually, the recorded Corsi improvements could have been achieved in a number of different ways, but the primary factors would most likely include some or all of the following:

1. Better linemates
2. Worse team (since we're using Relative Corsi)
3. More advantageous situations
4. Weaker opponents
5. Improved play

At a high level, we aim to determine which of these factors are the most common explanations for the recorded improvements, and to what degrees.

Better Linemates

A player could see an improvement in Relative Corsi simply by virtue of having better linemates. They could have been promoted to a better line, been paired up with a key offseason acquisition or return from injury, or might even find themselves on new teams. In fact, 12 of LEIP's 52 members began the season on new teams, and a smattering of others spent at least part of the prior season with different clubs.

The best way to measure whether a player is playing with a higher caliber of linemate is to look at the difference in the Corsi-based Quality of Teammates (QoT) measurement, and indeed 41 of the 52 players have improved QoT. The correlation coefficient between the improvement in Corsi and QoT among the LEIP is 0.55. It's natural to expect a good correlation, because whatever factors are helping the players in question perform better than last year may be helping their linemates do so as well.

Worse Team

Since we're dealing with relative Corsi, a player could look better simply by virtue of being on a team that's using weak players when they're not on the ice. Take Dustin Byfuglien, for example. Last year when he wasn't on the ice, guys like Marian Hossa, Jonathan Toews, Patrick Kane and the Stanley Cup champions were. This year in Atlanta when he's not on the ice, the Thrashers are using guys whose kids probably didn't even bother collecting their hockey cards.

In point of fact, Byfuglien's straight-up Corsi has actually gone down, meaning that Atlanta's first line isn't enjoying as much territorial advantage as Chicago's third line was last season. Only two other members of LEIP have seen their on-ice Corsi scores go down (and are thus benefitting from the decline of their teammates): Jonathan Toews and Boston's Mark Stuart.

For almost everyone in the LEIP, most of the explanation for the improvement in the player's relative Corsi has been improvements in their own on-ice Corsi score, not drops in the off-ice Corsi score. The correlation with a player's own on-ice Corsi score is 0.53. Now don't get us wrong, 40 of the 52 members of LEIP have seen drops on the off-ice Corsi, but the correlation is just 0.08, so it's really not fair to credit anyone other than Byfuglien with this explanation.

More Advantageous Situations

As Kent Wilson recently reminded us in his analysis of Bobby Ryan, "each additional offensive zone draw is worth about +0.8 in terms of Corsi." An increase in offensive zone starts could therefore explain at least some of a player's improvement.

Within LEIP, the correlation coefficient between the improvement in Relative Corsi and improvements in offensive zone starts is 0.33. 34 of the 52 are seeing more offensive zone draws, including Tim Jackman, Darcy Hordichuk, Kyle Chipchura and Kirstian Huselius, who are all being used mostly in the offensive zone, compared with last year's relatively even usage. One of the interesting exceptions is the aforementioned Stuart, who is starting in the offensive zone only 39% of the time, compared with 53% last season.

Weaker Opponents

Another way to improve your Relative Corsi is to be used against weaker opponents. As Tom Awad grazed upon in his Good Players Series, that can often mean you are also playing with weaker linemates, too, but in certain cases, like the Anaheim Ducks or the Vancouver Canucks, certain players take on the tougher minutes to make things easier on a select few.

Among the LEIP, against its 34 of the 52 that are facing softer competition, and the correlation between the Corsi-based Quality of Competition and the improvement in Relative Corsi is 0.20.

Improved Play

Naturally, there's always the possibility that they're simply playing better. If so, we would expect several players to be 24 or younger, when players experience the most dramatic improvements in play. However, the LEIP appears to have a rather normal distribution in ages, with only eight players 24 or younger, and 13 who are at least 30, like Rozsival.

It's not easy to measure how much of a factor improved play is, although we at least know that it is capped by what hasn't been explained by the factors above (i.e. not much). While there certainly appear to be a few players that are clearly having breakout seasons, like Byfuglien and Clarke MacArthur, most of them appear to be flying below the radar. In fact, two members of LEIP, Tim Connolly and J.P. Dumont, were listed among the season's top disappointments top disappointments by the Puck Daddy staff.

Adding it All Up

The numbers don't add up to 1.00 for at least two reasons: this was a rough and dirty study, and that there is overlap between these factors. Nevertheless, it serves our purposes nicely at a high level to look at cases such as Rozsival's.

Count: Proportion of LEIP having this factor
Corr: Statistical correlation to this factor

Factor           Count Corr
Better linemates 0.79  0.55
Better situation 0.65  0.33
Easier opponents 0.65  0.20
Worse team       0.77  0.08
Improved Play     N/A   N/A

The most significant factor in improvements in Relative Corsi appears to be better linemates, followed by being used in more advantageous situations, and against easier opponents.

In Rozsival's case, he certainly hasn't enjoyed better linemates since being replaced by Dan Girardi for top-line duty alongside Marc Staal, his offensive zone starts have budged by less than 1%, and his Quality of Competition numbers have actually gone up. What does this mean for Phoenix? Rozsival's improvement this season could actually be a legitimate consequence of improved play. If you ignore the salary cap side of the equation, the Coyotes might actually have made a marginal improvement, hopefully the type that will earn them their first postseason series victory since 1987.

Robert Vollman is an author of Hockey Prospectus. You can contact Robert by clicking here or click here to see Robert's other articles.