DiPS Game Score

I've been tinkering around with a pitching statistic for starters, and I think I'm ready to share it. It's a new take on an old stat called Game Score.

Game Score was developed by Bill James to give a single number to a pitching performance that should tell you how they did. I like the stat; it bases everything around 50, and naturally caps at right around 100. Here is the formula:

Start with 50 points. Add 1 point for each out recorded, (or 3 points per inning). Add 2 points for each inning completed after the 4th. Add 1 point for each strikeout. Subtract 2 points for each hit allowed. Subtract 4 points for each earned run allowed. Subtract 2 points for each unearned run allowed. Subtract 1 point for each walk.

Thanks to Baseball-Reference for the link.

While Game Score does give a pretty accurate guess as to how a pitcher did (the leaders yesterday were Shark and Kershaw at 86 each; Volquez' 24 brought up the rear), I had to distinct issues with it:

a) It does not penalize short outings. You can strikeout the first batter and end with 51 points, or go 6 innings, allow 3 runs, and end up with 46. 

b) It counts things that are out of the pitchers hands (earned runs, runs, and hits).

DiPS theory teaches us that hits come in more-or-less a random distribution that we can control only slightly. Thus, the pitcher's burden is just to get outs and reduced the number of balls in play or over the fence. It is with this in mind that I set to re-write Game Score.

First, I got the latest run expectancy matrix and calculated how many expected runs are saved, on average, by striking a player out (increasing outs by 1 with no station changes). The answer was .457. Then, I calculated the run expectancy of a walk (increasing the relevant stations by 1 with no out changes), and the value was .523. Lastly, I changed the bases-clearing, run-scoring change of the HR, and got a value of 1.77. I came to these conclusions:

A HR was roughly 3 times more valuable than a walk. A walk was slightly worse than a strikeout was good. The values roughly went like this: K – 3 points, BB – -4 points, HR – -12 points. This kind of makes sense: If you gave up a HR, then struck out the side, you had a bad inning, but not an awful one – at least you minimized the balls in play. Of course, it's possible you actually gave up 6 runs in that inning with a series of base hits, but that is somewhat attributable to luck. 

After that, I made a judgement call on how many points to give to outs. If a strikeout was worth 3 points, a regular out seemed to be worth 2 to me. This part could definitely be changed (and may be, to 3 points). 

The only thing left was to make sure that the average SP performance was roughly 50. I took my numbers and assigned the average performance last year to them (18 outs, 5 strikeouts, 2 walks, .68 HR). That came up as 35 points, so I added a baseline of 15 points.

The problem with this new stat is that there is no natural line to prevent a pitcher from getting over 100 points. Kerry Wood's 20-K CG SHO is 129 points, in this system. In my defense, I don't care so much about this. 

Which system is better? I'm not really sure. Today, I'm going to include every pitcher's game score under the old system and the new. You can decide for yourself which is better.

  Regular DiPS Delta STDEV
Kershaw 86 90 -4  
Samardzija 86 86 0  
F. Hernandez 80 81 -1  
Cueto 74 64 10  
Cain 71 71 0  
Sale 71 78 -7  
Chacin 67 49 18  
Kennedy 66 77 -11  
Verlander 66 58 8  
Weaver 66 55 11  
Anderson 63 59 4  
Niese 60 47 13  
Shields 58 57 1  
Burnett 54 63 -9  
Lester 54 58 -4  
Worley 46 56 -10  
Wainwright 42 69 -27  
Hudson 39 26 13  
Gallardo 37 26 11  
Hamels 37 20 17  
Sabathia 36 44 -8  
Volquez 24 33 -9  
  58.31818 57.59091 0.727273 11.17046
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