Introducing Win Shares
Hello again! Today, I'm going to introduce a new metric for player analysis in college hockey, called Win Shares. My Win Shares metric is based on Hockey Reference's Point Shares, created by Justin Kubatko. What I did was take what Justin did, and tweaked it around for college hockey, given the extra information we have available to us. I'll get into a basic description of Win Shares, as well as share what tweaks I made to it. For the sake of efficiency, I won't write out the whole formula here. If you'd like to see the full formula for yourself, it's available on Hockey Reference (www.hockey-reference.com/about/point_shares.html). Also, a quick note, the following tweaks were done for NCAA players. As little data that exists for the NCAA, even less is out there for USports hockey. The USports Win Shares metric mostly sticks to the original formula without my tweaks.
A basic explanation of Win Shares (or Point Shares), is that it attempts to quantify an individual player's contribution to their team in three facets of the game: offensive, defensive, and goalie. Skaters will have both an offensive and defensive win shares number, while goalies will only have the goalie win shares number attributed to them. It tries to boil down a player's different stat lines into one single metric for the purpose of comparison against other players that play in the same league (in this case, other college hockey players across the country). It isn't perfect by any means (i'll get into this later) and we have better metrics for analysis at the NHL level for evaluating performance. However, at the college hockey level, where data is limited compared to pro leagues, these numbers can shed some insight as long as you're careful about jumping to conclusions.
The first thing that I obviously changed was tweaking the formula so that it was tuned to team wins, rather than team standings points. I did this since college hockey doesn't have a standardized point system at the national level, so I adjusted the formula so that it's based off of the number of wins a team has, with a tie counting as half a win, just like it does to the NCAA.
The next thing I changed was in respect to the "Goals Created" stat used in the Offensive Point Shares metric. Hockey Reference says that an assist is worth half a goal for the sake of simplicity. I decided that I wanted to calculate the actual value of assist, and use that as my coefficient. Drawing off of the incredible work done by Shawn Ferris, Mike Murphy, and Dom Luszczyszyn, I decided to go with the same approach as their "Game Score" calculation. I totaled the number of goals and assists scored in the relevant season by every team. Then, you divide the total assists by total goals to get your assists coefficient. I did this for every season that I scraped, as I wanted to capture how much an assist was worth from season to season. For 2019/20, I calculated an assist coefficient of 0.579 for the men, and 0.586 for the women. This meant that an assist was worth a little less than 60% of a goal. In addition to calculating new assist coefficients, I also added Corsi For to the formula. I figured that I wanted to also capture the offensive output of players that were driving play, but not necessarily gathering points. In the 2019/20 season, the Corsi coefficient for both men and women was 0.051, meaning one shot attempt was roughly worth about 5% of a goal.
The last thing I changed was the proportion of team marginal goals against assigned to skaters, used to calculate Defensive Point Shares. In the original formula, it compared team shots on goal against to league shots on goal against. I changed it to team corsi against compared to league corsi against. I felt that using Corsi instead of shots on goal more accurately reflected a team's defensive capabilities. We were able to do this since we have corsi against data on the league and team level, just not at the individual level.
After all these adjustments, we are able to calculate our various Win Shares components. I use this to put into my player cards, which shows a player's season in context, showing both Win Shares numbers as well as rates for certain stats. All of these show percentile as well to compare it to other college hockey players. The stars in the cards are assigned based off of the percentiles, which each star adding another 20%. If a player has 5 gold stars in a certain category, that means he/she placed in the 96th percentile or higher in that stat. This was done to highlight the truly elite players in these categories. OWS stands for "Offensive Win Shares", DWS stands for "Defensive Win Shares", and TWS stands for "Total Win Shares", calculated by adding a skater's OWS and DWS. An example of a card is shown below:
I want to also address some of the cons of Win Shares. It doesn't take into account nearly enough to make it a stat similar to something like EvolvingHockey's WAR at the NHL level. The defensive side uses plus/minus to adjust individual players. We all know how bad of a stat plus/minus is compared to something even as simple as a player's CF%. Unfortunately, that's the absolute best we can get right now, with the only "advanced data" we get at the NCAA level is team CF and CA, and individual CF. There's no TOI or CA data individually available publicly, so we have to make do with the more traditional stats. Therefore, while this is the best we can do to boil down a college player's contribution into one number, we must be cautious when using that one number. Understanding it in context helps when making judgments on players. For example, goalie win shares tend to be inflated with respect to their teammates. Another thing to look out for is good players having low defensive win share numbers due to their team giving up more goals than usual. Win Shares can be a very helpful tool when evaluating, but it's honestly just a start to truly measuring a player's ability.
As a thought exercise, let's use Win Shares to determine our picks for the Hobey Baker as well as the Patty Kazmaier awards. First, for the Patty Kaz, we completely agree with the actual pick. Élizabeth Giguère was far and away the best women's DI player the whole season, and our data agrees, attributing 4.875 win shares to her! For the men, going strictly based off of Win Shares we would give the Hobey to Jeremy Swayman, Maine's stud junior goaltender. He racked up an astonishing 5.322 win shares this season. However, we do know that goalie win shares tend to be a bit inflated, something that is down to a matter of opinion how valuable goaltenders are at different levels of the game. Therefore, if you didn't want to pick a goalie, we would go with Bowling Green's Alec Rauhauser. He finished 2019/20 with 3.184 win shares, good for best at the DI level for forwards and defenseman.
Thanks for reading! I hope you like the new logos for the site! I decided to put to use what limited artistic ability I had to make the site look a little nicer. I hope to get the actual WS data up on the site ASAP, once I figure out the best way to go about it. I also hope to implement the code to calculate Win Shares for USports soon! Stay tuned!
7/29/2022 03:23:33 pm
Thanks for taking the time to share this
Leave a Reply.