In the hockey analytics community, Corsi and Fenwick are valuable tools that help us gain insight into possession. While they aren’t exact measures of possession, they’re indicators that help show which teams win the shot share battle as well which players help tip the scales in the possession game when they’re on the ice.

Unfortunately, those tools aren’t currently available to the public in women’s hockey at any level. With the exception of some outstanding work done by Carolyn Wilke in the NWHL’s inaugural season, little has been done to advance shot metrics in the women’s game.

SHOT METRICS

For those who don’t know, Corsi and Fenwick are tools used to measure shot attempts for individuals, units, and teams as raw numbers or rates, as well as the ratio of attempts between two parties. Why are these tools valuable? An easy way to grasp the value of shot metrics and metrics is to connect them to the concept that you need to have the puck in order to score a goal.

Corsi is the sum of a player or team’s shots on goal, missed shots on goal, and blocked shot attempts towards the opposition’s net, minus the same shot attempts directed at your own team’s net. So, it’s shot differential, but it counts shot attempts instead of just counting the shots that go into the net and the ones that are stopped by a goaltender. And if you’ve heard the term “Fenwick” before, it’s simply Corsi without the blocked shots — the logic here being that blocked shots are a skill.

The more shots you attempt, the more likely you are to score a goal; when you attempt more shots than your opponent, it stands to reason that you increase your chances of outscoring them and winning the game.

Of course, that is just a surface level explanation of shot metrics and their value without wading into the waters of shot quality and scoring chances. Even if you’re new to analytics or are intimidated by stats, it should be easy to embrace the idea that not all shots are created equal and that attempting more shots than the opposition will, generally speaking, lead to scoring more goals.

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Women’s Hockey Analytics Primer

CONCEPT

While working with the NWHL this season, I realized that when the league’s stat trackers record blocked shots they also record the players who attempted those shots. Shortly thereafter a light bulb appeared over my head.

My first thought was that the combination of shots on goal and shots blocked was a strange and less insightful cousin of Fenwick. However, upon looking over the numbers I was intrigued by what we could learn from this unique way at looking at shot attempts in the NWHL.

Note: “blocked shots” and “shots blocked” mean different things — shots blocked refers to the number of shot attempts by a player that were blocked by opposing skaters.

As I continued to look at the numbers and the rates of this new “stat” I needed a name for it. My first thought was to name it after a retired player. The natural choice was NWHL legend Kelley Steadman who averaged a whopping 8.78 SOG/GP for the Buffalo Beauts during her two-year career. From the neutral zone forward, she was a tornado with a hockey stick.

Steadman is an NWHL champion, a CWHL champion, a two-time NWHL All-Star, and an All-Star Game MVP in addition to being a prolific goal-scorer and high-volume shooter during her playing career. Naming a stat that measured shot attempts in NWHL games after the assistant coach of Mercyhurst University seemed all too appropriate. She even gave the idea her nod of approval. So, “Steady” is the name of this metric and “KSt” will be its shorthand.

KSt = shots on goal + shots blocked by opposition

Much like many other tools we use to analyze statistics in women’s hockey — see: Game Score — Steady is very much a MacGuyver’d version of tools that have proven to be valuable in NHL analytics. It’s not Corsi and it’s not Fenwick; it’s a different and likely less-insightful shot metric than its cousins.

FLAWS

Well, where do we begin?

First and foremost, it’s essential to clarify that all “SOG + Shots Blocked” data made available by the NWHL is for all situations and not specifically for even strength or 5-on-5 play. Having a breakdown of Steady events by strength would be far more valuable than having one value that represents Steady in all situations. We know this because it’s true for similar events like Corsi and Fenwick.

Steady will be heavily influenced by special teams play for players, units, and teams. So, a team like the Buffalo Beauts, which has been shorthanded 52 times while only having 38 power play opportunities of their own as of Dec. 1, 2019, will have a heavily-skewed team Steady and its players may have a lower iKSt/GP relative to skaters on other teams.

We can infer that because it stands to reason that teams attempt far fewer shots than the opposition when they are killing penalties. Generally speaking, the power play represents an opportunity to attempt more shots — and to have more shots go on net or be blocked by the opposition. Last season, NHL skaters averaged 5.71 blocked shots per 60 when they were shorthanded; NHL skaters averaged 2.91 Blk/60 at even strength (data from naturalstattrick.com).

Team “Steady” Through 12/1/2019

As with all stat tracking, we also need to acknowledge the existence of and potential for human error. For example, numerous skaters have SOG and Shots Blocked totals that don’t add up to their “Shot” total. These discrepancies could be the result of trackers including shots that miss the net or shots that hit the post in their shot total for individuals but it’s most likely that they are errors.

Regardless of the answer, it’s a clear indication that different trackers have different ways of tracking events (which is perfectly understandable and applies to all humans who observe and attempt to record events). As a result, Steady focuses specifically on SOG and Shots Blocked without taking into account the NWHL’s “shot” statistic.

Before the season began, I created a best practices document for all of the league’s trackers. In that document I defined some key terms for the statistics that were being tracked this season. It is because of this that I have more faith in the NWHL’s blocked shot data than I did in previous years. Tracking stats is not easy and I am deeply grateful for the good work that they do.

Any shot attempt in the direction of the goal that is blocked by an opposing defender who is not the goaltender is a blocked shot. A defender may be credited for a blocked shot regardless of which part of the body or what equipment the shot hits.

Note: If a puck is partially blocked by a defender but the goaltender must stop the puck, the defending skater should not be credited with a blocked shot.

The bottom line is that there’s no escaping human error in stat tracking because events can be subjective. It’s no secret that NHL trackers in some markets are more liberal with their definition of what should be credited as a hit. Fortunately, the human error we can’t get away from for all stats this season will be helped along by the NWHL’s 24-game regular season — the longest yet in league history. This larger sample size should help reduce how errors in tracking influence what we stand to learn from Steady and other stats like takeaways, giveaways, and blocked shots.

In short: Steady leaves a lot to be desired, but it can still prove to be a useful tool.

APPLICATION

Even a shot metric that has only one additional layer of sophistication beyond shots on goal can tell us a lot about what’s happening on the ice.

If you refer to the table above that displays team Steady rates for, it should come as no surprise that Boston is absolutely dominating in attempted shots that went on net or were blocked with a rate of 60.5 KSt/60. However, it’s intriguing to see that the Minnesota Whitecaps’ are closer to Boston in KSt/60 than they are in SF60.

So, what can we glean from this information? The Pride and Whitecaps are very close in team penalty differential and entered the season as the two clear favorites to win the Isobel Cup, so that makes a comparison of these shot and Steady rates even more valuable.

In addition to getting more shots on net, the Pride have also had more success at getting shots past defending skaters than the Whitecaps and the NWHL’s other three teams. If we look at the ratio of SOG to KSt, the Pride lead the pack with 43.3 percent and Minnesota comes in at third at 42.0 percent. Unsurprisingly, the Connecticut Whale are in last place in the ratio of SOG to KSt with a success rate of 40.47 percent. All of this lines up with the eye test and the current standings.

It’s also unsurprising to see just how many of the players who are currently leading the league in iKSt (individual Steady) play for the Pride and the Whitecaps. Furthermore, the league’s leaders in iKSt/GP (individual steady per game) reads like a list of the most productive and dangerous skaters in the NWHL with McKenna Brand (BOS), Nicole Schammel (MIN), and Jonna Curtis (MIN) as the top-three.

The Top 30 Skaters in iKSt (individual Steady, all strengths)

The most noteworthy players missing from the top-30 in the table above are Beauts rookie Brooke Stacey and Pride veteran Emily Fluke. Stacey is one of eight players in the league with six or more goals, but has a rate of 2.56 KSt/GP. Fluke is an All-Star and a key cog on Boston’s high-scoring third line, but her KSt/GP sits at 2.78. Both are among the league’s best players, but Steady isn’t meant to measure the quality or skill of a skater.

The best current application of Steady is to measure shot volume for teams, lines, d-pairs, and individuals. Steady goes beyond the standard of SOG/GP, which is used in my NWHL game score and has been part of the gold standard for identifying the league’s most dangerous offensive players for four years. Furthermore, it can give us some insight into which players have the most success getting shots past defenders and on net which is a skill in its own right.

Eventually, we can test Steady to see if it is a better tool for predicting performance than SOG. This would make it a strong candidate to improve the existing NWHL Game Score, which, along with the work I’m doing this season to track 5-on-5 on-ice goal differential, should add a few more valuable tools to what is admittedly a modest looking tool belt. We will learn more about what Steady can offer as a tool for analysis and evaluation as the season progresses.

All data courtesy of nwhl.zone and the author’s own tracking.

Disclosure: the author of this piece is currently employed by the NWHL.