Summing up Game Scoreby Matt Hunter
April 18, 2013
I'm on a bit of a pitcher evaluation kick at the moment. Just a couple of days ago, I wrote about crowdsourcing balls in play at Beyond the Box Score.
More importantly, two weeks ago I had an idea: instead of measuring starting pitching performances on an inning or plate appearance basis, why don't we evaluate them on a game-by-game basis? Since (team) wins are the end goal of a pitcher, and since each game is basically independent, we could evaluate an entire season simply by evaluating each start, and summing them up.
So how do we evaluate a single start? Traditionally, we have used pitcher wins. Then, those who wanted to ignore the effect of the pitcher's team offense thought of the Quality Start. But do we really want to say that a six-inning, three-run start (4.50 ERA) is quality? No is the answer. No we don't.
There wasn't a great way to evaluate a single start, so Bill James, doing what Bill James does best, created something called Game Score. Here's the formula for Game Score:
Game Score = Outs + 2*(innings completed after the fourth) + strikeouts - 2*hits - 4*earned runs - 2*unearned runs - walks + 50
It was a pretty good start, but far from perfect. Weighting earned runs twice as strongly as unearned runs seems arbitrary, as does counting only innings after the fourth. I won't get into the specifics of what's wrong with this Game Score, because it doesn't really matter for my purposes. But, because it will be a good reference, I'll show you the leader board for the sum of each pitcher's Game Score for each start in the 2012 season:
Looks like it passes the sniff test to me. Let's move on.
A couple years ago, Tom Tango introduced a few alternatives to James' Game Score, each one based on a different method of evaluating pitchers. Let's summarize them.
The first new version of Game Score cares only about runs allowed. It's essentially the Game Score version of RA9. Here's the formula (again, as formulated by Tango):
Game Score = 6.4*IP – 10*R + 40
And the 2012 leader boards for total Game Score:
Strikeouts and walks
Here we have the other end of the spectrum; instead of considering only runs allowed, this version is going to be based only on strikeouts and walks, and nothing else. It's basically the Game Score version of kwERA.
Game Score = 0.4*IP + 3*(SO–BB) + 40
And the leader boards:
See the previous version, but add home runs, and you have the FIP version. There's really not too much else to say. As always, Tango's formula:
Game Score = 2.5*IP + 2*SO – 3*BB – 13*HR + 40
Last one! This time, we're going to use a simplified version of linear weights, looking only at walks, hits and home runs.
Game Score = 8.4*IP - 3*BB - 5*H - 8*HR + 40
Now, it's almost certain that none of these versions of Game Score is perfect on its own. However, as Tango said in the article a few years ago, we can assign weights to each one depending on our goals or preferences. Unfortunately, right now, I'm not sure how to do that. Maybe that will be a project for a future article. For now, I'm going to give you the average of all four new versions of Game Score.
This list looks good, but it is far from a perfect way to evaluate pitchers. It doesn't take into account park or league factors, which is incredibly important. However, if you're looking for a different way to evaluate pitchers that takes many different factors into account, this is something to consider.
There you have it. For your reference, here's a Google Docs spreadsheet of all the versions of Game Score for every pitcher who made at least one start in 2012.
Before I go, because I didn't do a whole lot of actual analysis, here are some of my ideas at the moment for where to go next with these data:
- Include park and league factors
- Combine these versions of Game Score with varying weights
- Convert Game Score to wins
- Look at total Game Score over a career
- Probably much, much more. Stay tuned!
Thanks again to Tom Tango for the inspiration and, honestly, most of the real analysis. Also thanks to James Gentile for the Retrosheet help.
Matt writes for FanGraphs, Beyond the Box Score, and the Hardball Times. You can contact him via Twitter @MRHBaseball or email.