The Astros’ pitching staff, specifically the starting rotation, has made headlines this season.
Entering the Memorial Day weekend, the Astros‘ starting rotation currently rates as the best staff in the game. And it is not really a contest.
Here are a few examples:
- 2.26 ERA (1st)
- 2.87 FIP (1st)
- 3.10 xFIP (1st)
- 9.3 fWAR (1st)
- 27 wins (1st)
- 22.9% K-BB rate (1st)
Need I go on?
In short, the Astros’ starting rotation is a key reason behind the team’s successful start. Although regression is likely, this staff’s performance from here on out will determine how successful is Houston’s bid in repeating as World Series champions. The same goes for the bullpen, which is one of the best in the game today.
So, what has been the root causes behind the team’s staff and its success story? Well, I think I can pinpoint at least one.
More curveballs and less changeups.
Travis Sawchik of FanGraphs recently posted an article about the Astros’ starting rotation and how it could be the “best ever*”. Here is one key sentence from Sawchik’s article on the Houston staff.
"As Morton went away from a softer approach, the Astros have abandoned the changeup, throwing an MLB-low 450 changeups entering play Thursday."
Yes, less changeups. Like Sawchik mentions in his article, the Astros do not throw many changeups. Between Thursday and Friday, Houston pitchers only threw four changeups to increase their season total to 454. To compare, the Blue Jays’ staff leads baseball with 1,288 changeups entering Friday. Lance McCullers (165) and Chris Devenski (116) clearly lead the way for changeups thrown by a Houston pitcher in 2018.
This point is backed up by usage data over at FanGraphs. For example, the Astros’ starting rotation threw a changeup 10.3% of the time in 2017. This season, the changeup usage has dropped by 2.7%. Although it is still early in the 2018 season, the decrease jumps out.
On a slightly unexpected note, the Astros’ bullpen has actually seen their changeup usage climb and curveball usage drop in 2018.
Of course, this information is not as alerting since Devenski, a reliever, is known for his changeup. It makes sense why there would be an increase in usage as Devenski has increased his usage of the pitch by 3% when you compare 2017 and 2018. Again, the 2018 season is only partially complete and these numbers are subject to change. But you can’t ignore the data even now.
As you can also decipher from the information above, the Astros’ starting rotation has utilized the curveball more often. Sure, only 1% more than last season, but noticeably higher if you go back a few seasons. This season alone, the Astros’ pitching staff has thrown 1,179 curveballs. Only the Indians have thrown more curveballs at 1,299. And this is includes a decrease of curveball usage by the bullpen.
Out of the Astros’ staff, McCullers has thrown the most curveballs by far at 412. In fact, McCullers uses his curveball 42.7% of the time. Charlie Morton has thrown 277 curveballs followed by Gerrit Cole at 185 and Justin Verlander at 149. And Houston has had success with the curveball as the pitch has held opponents to a .213 wOBA and a .173 batting average.
Both pitches have demonstrated improved results this season, especially the changeup despite decreased usage. But the Astros have taken a strength in curveballs and made it even better. The improvements for both pitches are impressive.
Looking ahead, the Astros are likely to continue in their practice to throw fewer changeups. The collective wOBA and batting average for a changeup is .281 and .234 across baseball this season. Regarding the curveball, the pitch has generated a .267 wOBA and .223 batting average. Though there is not much separation in the numbers, the curveball has been more effective. And the Astros are all about effectiveness. Of course, numbers can change, so this author is curious to see what the splits are later this summer.
**Statistics and information courtesy of Baseball Savant and FanGraphs**