In the past two weeks research that has taken likely more than two weeks to compile, FanGraphs (specifically Eno Sarris and Daniel Schwartz) has briefly teased their Arsenal Scores (found here in Pt I and Pt II )This of course has no allusion to the English soccer/football club Arsenal and the results of their games, but instead these scores are a way to discuss and evaluate pitchers.
The metrics we have to evaluate pitcher performances are light years (which is a measure of distance, not time) beyond where we once were in the medieval age of Win/Loss records and a little further into the enlightenment of ERA. Fielding Independent Pitching strips away the volatility of balls in play and tries to express that a pitcher has little (or none in this case) control with what happens once the ball leaves their hand. Expected Fielding Independent Pitching (or xFIP) goes even further with that notion and assumes the pitcher had a league average home run rate (another volatile result). On perhaps the most inclusive, perhaps extreme, end there's Skill Interactive Earned Run Average (SIERA) which includes batted ball data.
It's likely there in some form, but you should notice that all of the above metrics don't expressively consider the most important skill-set of a pitcher: their pitch types and the skill of those pitches. Enter the Arsenal Score.
Here is Sarris' explanation of this newly proposed metric:
So, to that end, I've taken each pitch type and looked at only those pitchers that have thrown 100+ in each of those types. I've summed the ground-ball and swinging strike rates for each pitch, and then found the standard deviations. I've given each pitcher a z-score for his ground-ball rate and swinging strike rate on each pitch type. Then I've summed the z-scores for each pitch type, and then for each pitcher.
What we should be looking at is an Arsenal Score. With this way of looking at things, it's possible to have one dominating pitch and still score well. Or a group of lesser pitches that are all positive.
Z-Score is a measure of standard deviations above the mean either positive or negative. Two standard deviations above the mean would be expressed as a z-score of 2. Generally anything above 3 z-scores is considered an outlier.
In the second piece on the Arsenal Score, Daniel Schwartz introduced whiff% and groundball to flyball ratios into the data.
Using BP's PITCHf/x Leaderboard (100-pitch qualifier) I first found each pitch type's Whiff/Swing and GB/FB z-score. I then weighed each z-score by swinging-strike's (.62) and GB/FB's (.27) average correlation to ERA, SIERA and xFIP for all pitchers over 70 innings pitched (my lazy attempt to omit relievers). What is not incorporated and should be in the future, is differentiating weights for each pitch type. For example, groundball induction is a more important requirement for Sinkers; Sliders and Change-ups should induce more whiffs as we know from these Pitch Type Benchmarks.
The seven pitch types incorporated are Fourseamers, Sinkers, Cutters, Curves, Sliders, Change-ups and Splitters.
Below, we'll find the 2014 Royals starting pitcher Rep.Scores, Rep.Score ranking, and 2014 peripherals as well as the score for newly signed Royal Edinson Volquez.
A wide range here. Ventura is a promising young pitcher and for a Royals fan he can optimistically be found near the top-10 of all pitchers. Newly signed Volquez and newly departed Shields find themselves roughly in the middle of the group and their Rep.Score falls close to the average of 0. The second half of the group find themselves well below the mean of the group with Guthrie being ranked near the very last of pitchers.
Now broken out by pitch type.
There's likely to be more on fine tuning and tweaking of the Arsenal/Rep Scores eventually, but for now we've got a rough view of the per-pitch type evaluations for some Royals pitchers.