After losing our best pitcher from 2018 to free agency, Zack Greinke getting older, Taijuan Walker still recovering from Tommy John surgery, and down years from Robbie Ray and Zack Godley, it might be pretty easy to feel pessimistic about our starting rotation this year.
However, while we have lost a true ace in Patrick Corbin, the rotation for 2019 is still looking to be good, with FanGraphs rating it slightly above average with a projection of 11.2 fWAR for 2019 (15th-best).
But could it be better than that? The answer is a surprising yes. It’s by no means a guarantee and will need some luck on the health front due to a lack of depth, but the Diamondbacks have 4 average-or-better starters already and a fifth that is a wild card, with plenty of upside to boot.
Let’s use some predictive stats from last year to take a look at their 2018 performances:
Dbacks 2018 Rotation xK% and xBB%
|Player||xK%||2018 K%||Diff||xBB%||2018 BB%||Diff|
|Player||xK%||2018 K%||Diff||xBB%||2018 BB%||Diff|
What we’re looking at here are the “expected strikeout rate” (xK%) and “expected walk rate” (xBB%) and comparing them to the actual results. xK% has an R-Squared (R^2) of 0.931, which means it is extremely strong at predicting the true outcome. So if a player were to have a strong divergence from their xK%, it would mean that they are extremely likely to regress towards this predicted number. The xBB% R-Squared isn’t quite as strong - 0.77 - but that’s still much higher than most other baseball predictors.
So what’s the take away from this? Zack Greinke outperformed his peripherals last year, but the other three listed all underperformed, both for stirkeouts and walks. Now, the differences are pretty small, to the point that the results are likely within the margin of error, but it does yield two conclusions:
- The results were mostly in line with the peripherals, meaning that Ray and Godley’s strikeout rates last year were real (Steamer, for instance, is calling for a 2% regression to Godley’s K% for no apparent reason).
- Some positive regression would be REALLY good for Ray and Godley’s walk rates, both of which were around 1% higher than expected.
That last bullet is surprising, considering we had the best catcher defense last season with regards to framing. Now, while this analysis does yield a bit of optimism, dropping your walk rate by 1% isn’t the difference between a 4.50 ERA and a sub-3.00 ERA. And unfortunately, we don’t really have any stats to strongly indicate a breakout to any of our pitchers... YET (we’ll need 2019 data for that). But we can go through our rotation and see where the potential lies.
(All projections below are using FanGraphs Depth Charts)
2019 Projection: 192 IP, 3.84 ERA, 3.89 FIP, 2.8 fWAR
FanGraphs (and really, everyone) has been calling for Greinke to regress for the last couple of years now but he keeps proving everyone wrong. His FB velo continues to drop and he might be below 90 MPH for good, but that didn’t seem to matter too much last year. He’s starting to give up more homers, but his strikeout and walk rates are still strong. Despite the decrease in FB velocity, he’s still seeing double-digit whiff rates on his slider, curveball, and changeup:
All three of these pitches generate swings over 50% of the time while his fastball was only swung at a career low 32.98% last year. As long as he keeps getting swings and whiffs on his secondary pitches, Greinke is going to be a good pitcher.
We all know Greinke’s upside - he could put together a 5 WAR season and has done so plenty of times. The chances of him doing so at this point are quickly diminishing. For the sake of this exercise, Greinke is more about avoiding a decline rather than pitching to his upside... but you never know.
2019 Projection: 159 IP, 3.80 ERA, 3.79 FIP, 2.6 fWAR
It’s a bit surprising to see Robbie Ray projected to be better than Greinke given recent results, but it also makes sense considering how dominating Ray’s stuff can be. Of course, therein lies the problem: Greinke is extremely consistent and Robbie Ray is anything but.
Again, this is another example where we all know what Ray’s potential upside, it’s just a matter of realizing it. When Ray first broke out two years ago, it was simply a matter of cutting his walks down while he developed as a young pitcher. Sounds easy, right?
Unfortunately, Ray has done the opposite. His walk rate has increased each year - from 9.2% in 2016 to 10.7% in 2017... to a massive 13.3% in 2018. Ouch. Combine that increasing hard-hit contact and homer rates and it’s been a complete disaster for Robbie Ray, right?
Surprisingly, no. After an egregious .352 BABIP in 2016, Ray has posted BABIPs of .267 and .292 the last two years with only small increases in the home run rate. And still maintaining that absolutely elite strikeout rate. He had a 2.89 ERA in 2017 and a 3.93 ERA last year, so the resutls have still been good.
It’s been said over and over, but we know what needs to be done. If he can get his walks down to 2016 or 2017 levels and cut down the home runs a bit, he’s going to make Patrick Corbin look like a #2.
There is some massive untapped potential with Ray. Out of 140 pitchers with at least 100 IP last season, Ray had the 6th-lowest swing rate. Yet he still had the 8th-best K%, even better than Corbin. If he starts to control things more, batters will have to swing more. And with more swings will come more strikeouts.
2019 Projection: 160.0 IP, 4.18 ERA, 4.10 FIP, 2.0 fWAR
This story is getting old. On one hand, it’s really amazing that we had 4 pitchers in our rotation that were all among the best starters at K%. Over the last two years combined, Ray was 3rd, Corbin 23rd, Greinke 27th, and Godley 29th in K% among MLB starters. That’s really impressive.
On the other hand, can we get some damn consistency? I’m looking at you, Ray and Godley. We all saw Zack Godley breakout in 2017, in which certain authors compared him to the great Brandon Webb, and for the most part, it’s all still there. He had the 23rd-best whiff rate among starting pitchers last year (and his xK% largely validates it) and the 7th-best groundball rate. As seen in the article linked above, this is an extremely uncommon combination that usually leads to great results. We saw the great results in 2017 but we didn’t quite see them in 2018.
Godley in 2018 just seemed to be trying too hard. He was falling off the mound constantly, struggling with his command, and just absolutely imploding randomly in the middle of games. Among all of this commotion, it caused his walk rate to jump 2 whole points. And xBB% says it was largely to be believed, so there was obviously something intangible that caused this spike (which we saw from that wildness). But Godley really did sort things out in the second half of the season:
1st half: 22.8% K%, 11.2% BB%, 4.27 FIP
2nd half: 24.2% K%, 8.8% BB%, 3.16 FIP
That second half line is good. Really good. It’s also very similar to his 2017 breakout season, when he had a 26.3% K% and 8.5% BB%. If he continues pitching like second half Godley (much like how 2018 Corbin pitched like second-half 2017 Corbin), he will likely be the best pitcher on the staff next year, barring a breakout from Ray or Weaver.
Don’t sleep on Zack Godley. He’s really good and he quietly turned things around without a lot of us noticing.
2019 Projection: 132 IP, 4.43 ERA, 4.30 FIP, 1.5 fWAR
Luke Weaver is hard to project because, well... this author never watched him pitch last season. And a quick glance at his 2018 stats isn’t terribly promising.
Weaver was a former top 100 prospect with the St. Louis Cardinals who looked really good in 2017 before really falling off in 2018 in a larger role.
2017: 28.6% K%, 6.8% BB%, 3.88 ERA, 3.17 FIP
2018: 19.9% K%, 8.9% BB%, 4.95 ERA, 4.46 FIP
That’s a pretty huge difference in just the manner of one season. That being said, Weaver was only pitching in his age 23 and 24 seasons, so there is tons of room to develop. The scouting report on Weaver is that his fastball isn’t great but he has an excellent changeup. He also has a very fast arm, which tends to mean he can throw hard breaking pitches with good spin. But so far, he hasn’t really been able to develop a cutter or a curveball to great success.
However, the Diamondbacks pitching development seems to be doing extremely well these last few years so maybe coming to AZ will be a good thing for Weaver.
Is his 2017 repeatable? It might be possible. His xK% for 2017 was 26.9%, which is significantly better than the 19.9% he posted last year. For what it’s worth, his xK% last year had him closer to 21% so the arrow is certainly pointing up for Weaver. It’s hard to say exactly what his upside is without watching more of him, but it seems like he does have the potential to be a pretty good pitcher. But he could also go the Shelby Miller route (oh god, please no). Time will tell.
2019 Projection: 118.0 IP, 4.57 ERA, 4.49 FIP, 1.0 fWAR
This author really has no idea what to make of Merrill Kelly at this point. The projections are better than what one might expected for a late-20-something coming over from the KBO (which is considered a step below the Nippon Professional Baseball league), but still not great. So where can we look for upside?
It’s hard to project players from the KBO because the league plays so much differently than in the US. Contact rates are considerably higher and therefore strikeouts are less common. Yet, Kelly managed to spike his strikeout rate from 6.8 K/9 in 2016 to 9.0 K/9 in 2017. Usually this means either one of two things:
- A random, unsustainable overperformance
- Some sort of meaningful change
Obviously, we want it to be number 2 as this would mean that he could have some level of success in the MLB. However, the stats and data for the KBO leagues are very limited, so it’s hard to figure out what happened. The Diamondbacks seemed to have done their due dilligence and seem to be on board with whatever Kelly did to improve.
For two years and only $5.5 million, this is a low risk investment for the Dbacks. Chances are that he doesn’t have great success at the MLB but... you never know. He’s our #5 and only below-average starting pitcher at this point, so the bar isn’t high. Let’s see what you got.