Currently, three Dbacks pitchers sit among the MLB’s top 20 in bWAR. Greinke and Ray should be obvious. However, that third pitcher isn’t Taijuan Walker or Shelby Miller. It’s Zack Godley. The same Godley that bounched between the rotation and the bullpen and the MLB and AAA over the past two seasons. With a 2.53 ERA and a 3.18 FIP, Godley has been fantastic this season.
So what changed? The easy answer: Godley has vastly improved his K% and GB% in essentially one offseason. And the changes are huge: his K% has gone 17.9% to 23.6% and his GB% has gone from 53.8% to 59.9%. And this is where things get interesting - the combination of high GB% and high K% is often very rare. Very rare, in fact, that a certain Brandon Webb was once among the best pitchers in baseball (1 Cy Young and 2 runner-ups) because of just this skillset:
I’ve highlighted Zack Godley in red and Brandon Webb in Green (they’re both on the very right side of the graph). There are 1,271 qualifying pitcher-seasons on this graph. Brandon Webb was clearly an outlier - that much was obvious. But so far, so is 2017 Zack Godley.
Godley’s GB% is a bit lower than Webb’s were, but he’s also putting up a higher K% than Webb ever did. Let’s compare how they stand out when compared to their league-years.
Before we get into the next part of the analysis, I’m going to get into a concept known as “z-scores”. A z-score is a number that indicates how many standard deviations a data point is from the mean. A z-score of 0 means that the data point is equal to the mean; a z-score of 1.5 means the data point was 1.5 standard deviations above the mean; a z-score of -2.3 means the data point was -2.3 standard deviations below the mean, etc.
In a normal distribution (e.g. bell curve), the standard deviations define what portion of the population is represented:
From -1 to 1, 68% of the data is represented.
From -2 to 2, 95% of the data is represented.
From -3 to 3, 99.7% of the data is represented.
So, if you have a z-score of 2, this means that you are in the top 2.5% of the population (or if it was -2, that would be the bottom 2.5%). This is very similar to percentiles.
This concept is actually used in baseball, mostly by scouts. The 20-80 grading scale is exactly this. 50 is considered “average” and therefore would be a z-score of 0. Scout grades of 40 and 60 would be -1 and 1, respectively. 30 and 70 become -2 and 2, 20 and 80 becomes -3 and 3. In other words, the scout grading scale is another way of representing z-scores (to simplify, if a scout says a player has a 70 grade tool, they are saying that the player is roughly in the top 2.5% when it comes to that talent).
Now that I’ve explained z-scores, I am going to derive zGB% and zK% for Webb and Godley. This is going to compare their rate stat versus the league averages for the respective year. Here’s how they look:
Webb vs Godley, zGB% and zK%
Both Webb and Godley have an elite GB% and strikeout rates a little above league average. However, Webb’s GB% was still quite a bit higher than Godley’s, equivalent to being a true 80 grade groundballer.
Essentially, Godley is Brandon Webb Lite. He’s got a very rare combination of grounders and strikeouts, but his grounder game just isn’t at the same level as Webb is. Two games ago, it was hovering at 64% and while I don’t really think it’ll bounce back up, we still have to give time to see where Godley ends up.
But let’s put into perspective what this means. With Webb, having a zGB% around 3 and a zK% around 0.5 made him one of the best pitchers in the league. Godley’s zGB% is still amazing - are there any other comps that we can make for Godley?
Godley zGB% and zK% Comps
There’s a few lessons to be found here. First, it’s really hard to find a comp to Godley - this is a very rare breed of pitcher. Second, it looks to be VERY difficult to repeat this kind of season - the most magical part of Brandon Webb is that he was able to do this every year for six seasons.
But the last lesson? Pitchers that are able to combine elite GB rates with above-average strikeout rates tend to have all-star caliber seasons. So even though Godley isn’t quite Brandon Webb, he is still looks to be a very very good pitcher.
The real question now: what can Godley sustain and can he develop himself going forward? Between his sinker and his elite curveball, Godley looks to be able to sustain good GB and strikeout rates, but just how good will they be? I would say that he looks to be at least a #2 going forward. But Webb didn’t turn into the ace that he was until he developed that changeup.
Godley is only 27 and still has room to grow. Does Arizona have another potential ace in the making?