Zack Greinke: Should We Be Worried?

As I write the Astros are all but a total lock for the playoffs in 2020. The Astros have to lose all three of their remaining games, and the Angels have to win all three of their remaining games, for the Astros to fail to make the playoffs. Zack Greinke, probable Hall of Famer, will surely be the #1 guy in the Astros playoff rotation.

Overall he’s having a good season. In 12 starts his ERA is a slightly better than league average at 4.03. But according to Fangraphs his peripheral stats predict some improvement. His xFIP comes in at 3.50. His SIERA is 3.79.

Statcast numbers say otherwise. Greinke’s WOBA is .289, but his xwOBA is slightly worse, .313. But Zack’s wOBA has always beaten his xwOBA, a career .274 as opposed to a career xwOBA of .294. League averages of wOBA and xwOBA are .317 and .323 respectively.

At nearly 37 Greinke is not having his best season, but he’s still better than average by most traditional or advanced stat measures. But here’s why there’s some worry about Greinke going into the playoffs. It’s his September starts.

In August Greinke’s numbers looked like this:

ERA: 2.19...FIP: 2.51...xFIP: 3.68...SIERA: 3.83...WHIP: 0.86...Exit Velocity: 85.4

In September these are the numbers:

ERA: 6.08...FIP: 3.07...xFIP: 2.86...SIERA: 3.26...WHIP: 1.43...Exit Velocity: 87.7

If all you looked at was the first statistic, ERA, then you’d say it’s time to panic on Greinke. Six runs per nine innings won’t cut it in the playoffs, especially with the slumping Astros offense.

But look at the other stats and you’ll see that Zack has been pitching into some bad luck this month. No doubt, the 2.19 ERA in August was unsustainable based on xFIP and SIERA calculations, but Greinke is clearly pitching way better than 6.08 in September. In fact, xFIP and SIERA say he’s better in September than August.

So what gives?

In August Greinke’s BABIP (batting average of balls in play) was .257. (career average of .294) Even though his K% was a relatively low 23.4%, his Batting Average Against was a very low .206. Granted that the exit velocity of batted balls was a little less in August than September, nonetheless batted balls were finding gloves at a very high rate. Plus, Greinke was pretty lucky about keeping baserunners from scoring. The Left on Base Percentage was 79.5%.

In September, Greinke’s BABIP is .403. That’s terrible luck. As a result, the Batting Average Against is .310. And the LOB% is only 61.7%

In September Greinke’s FIP- is 70. That means his FIP is 30% below league average. But his ERA- is 142 in September. That’s 42% ABOVE average. Greinke’s had a bad month results-wise. But that doesn’t mean he’s been pitching badly. His K% is considerably better in September than August, 27.6%, while maintaining a 2.6% BB%.

A deep dive into Statcast revealed this one disturbing feature of Greinke’s pitching this year. The wOBA on his changeup was .221 last year. It is 1.052 this year. On the other hand, Brooks Baseball has another take, assigning only a .270 SLG% to Zack’s changeup this year. Trouble with Zack is, it’s hard to tell sometimes exactly just what pitch he’s throwing. His changeup is almost the same speed as his fastball. But using Statcast, year to year, apples to apples, Greinke may be having some trouble with his changeup this year.

But that’s a quibble. Or maybe a quibble. Big picture is Zack Greinke’s troubles in September represent small sample size misfortune for the most part. That doesn’t mean his bad luck will automatically change come playoff time, but chances are he’ll still be Zack Greinke when it’s money time.