Checking in on Adam Wainwright’s Curveball

I have a favorite pitch in the majors. As someone who hopes to illuminate interesting aspects of the game of baseball, I wish I could say my favorite pitch was an obscure off-the-board pick that you had never previously considered – a pitch by an obscure reliever or an up-and-coming rookie, perhaps — but in reality, my favorite is classic and unoriginal. The pitch that makes me go weak at the knees like no other is Adam Wainwright’s curveball.

As a baseball fan of a certain age, I’ve recently found myself facing the mortality of the seminal baseball figures of my formative years. From The Kid’s enshrinement in Cooperstown to the imminent retirement of Alex Rodriguez to the 3,000th hit of a player from Japan who I swear won the Rookie of the Year award just a few years ago, my baseball life has been inundated recently with baseball reflections and farewells. When a 34-year-old Adam Wainwright posted a 7.16 ERA through his first five starts of the season, part of me wondered if I would also be saying goodbye to my favorite pitch sooner than later. However, since the start of May, things have turned around significantly for Wainwright.

As the season has progressed, Wainwright’s results have steadily improved to the extent that he now has a 2.74 ERA and 24.1% strikeout rate over his past 11 starts. However, one thing that hasn’t kept pace with his improved results is the performance of his signature curveball. By our pitch-type linear weights, the run value of his curve per 100 thrown is at the lowest mark since 2007 — his first year as a starter. Opponents have posted a 64 wRC+ against the pitch this season, which sounds reasonably good until you note that opponents have registered a minuscule 26 wRC+ against the pitch over his career. Is this a fluke, or has Wainwright’s recent resurgence happened in spite of the fact that his curveball is in decline?

To evaluate the performance of the pitch, I first looked at two key indicators: whiffs per swing and grounders per balls in play. If these peripheral stats remained stable, it would indicate to me that batters were performing as expected against the pitch and the declining results-based performance of the pitch was a fluke.

Here’s what the whiff/swing metric showed. The chart on the left shows whiff/swing against Wainwright’s curveball over his career and the one on the right shows just the 2016 season by month. (Note: I omitted August for sample-size reasons.)

The overall trend is alarming. After the pitch induced whiffs on 35-40% of swings for the better part of a decade, the whiff/swing on Wainwright’s curveball has dropped to 28.2% this season. However, the in-season trend is obviously more encouraging. During the month of July, it was back in its typical range over the 35% threshold.

Now let’s look at ground balls per balls in play over the same time period:

Same thing. There’s an unsettling overall trend where the results against the pitch have been well below Wainwright’s standards on the season as a whole, but the 2016 graph allows for the possibility that the pitch has improved as the season has progressed.

In digging deeper for potential causes of these changes in performance, there are two notable candidates: one that’s moderately discouraging and one that inspires hope. Let’s start with the bad news first, which is the pitch’s velocity. As you might expect for a 34-year-old pitcher, Wainwright’s velocity is in decline. Fortunately, he’s been able to maintain velocity on a fastball, which has averaged around 90 mph for much of his career, but the curveball velocity has had a different trajectory.

Again, his career chart is on the left and his 2016-only chart is on the right. You can see that his overall curveball velocity has returned to levels common for earlier in his career. However, the chart showing the steady decline during the season is a bit unnerving. In fact, there’s been a steady velocity decline across  his full repertoire during the 2016 season:

Wainwright’s curveball is not a power pitch and, as a result, the loss of a tick or two of velocity on its own isn’t terribly discouraging. But the fact that it’s part of a larger trend brings home the inescapable reality that we’re talking about a pitcher in his mid-30s who is unavoidably on the down swing of his career.

Onto the good news. One of the more troubling features of Wainwright’s curve over the start of the season is the frequency with which he has left them over the plate. Using Baseball Savant, I generated curveball location charts of Wainwright’s past three full seasons and the current season:

This year the pitch has been living up in the zone much more than is typical for Wainwright. Now take a look at the location of the pitch as the 2016 season has progressed:

In the month of July, he’s been commanding the pitch to the lower part of the zone with increased regularity. The fact that this trend has been accompanied by increasingly strong results in whiffs and ground balls induced provides optimism that his curve is returning to form.

Adam Wainwright has looked increasingly like himself as the season has progressed. This is fantastic news for a Cardinals team which finds itself in a strong position to win a wild-card spot. If he continues to build upon his recent resurgence, he can take his spot as the de facto veteran ace of the team and pitch in that sudden-death game – although teammate Carlos Martinez might have something to say about that. Regardless, there’s been a stay of execution for my favorite pitch and, for that most selfish of reasons, I’m grateful.