I got the idea for this topic after watching Stephen Strasburg carve up right-handed batters in the NLCS with changeups. I’ve always loved a good right on right or left on left changeup. Just from what my eyes tell me, it’s an effective pitch when executed. It’s not a common strategy though, across the league, about 15% of pitches to opposite-handed batters (OHB) are changeups, while only about 5% of pitches to same-handed batters (SHB) are changeups. I decided to dig a little deeper into the numbers to determine whether pitchers are optimizing their changeup usage.
First off, let’s talk about pitching strategy. So while pitchers’ arsenals vary wildly across the league, the most common pitch mix for a starting pitcher is Fastball (I’m going to lump all fastball types together for this exercise), Slider, Curveball, Changeup. Sometimes the pitcher will have just one of the two breaking balls or have a cutter instead of a slider, but FB, SL, CB, CH is the standard.
For the generic pitcher, the fastball the primary pitch and used over 50% of the time. Opposite-handed batters have a decent (about .015 wOBA) platoon advantage against fastballs, but the fastball is such a necessary pitch for most pitchers that it’s usage is almost identical (about 52% for each) versus SHB and OHB. Sliders have a significant (about .028 wOBA) platoon advantage against SHB and you see that in how sliders are used. Pitchers threw sliders 23% of the time against SHB and just 13% of the time against OHB in 2019. The slider is often the primary out pitch against SHB. The curveball on the other hand has only a slight (.010 wOBA) platoon advantage against SHB and is less effective against those batters than the slider. So it’s used a little more against OHB (11% vs 8%) usually to steal strikes and generate groundballs in the general MLB population. However, pitchers with really good curves use it frequently to both OHB and SHB since it’s not really a pitch with a significant platoon advantage.
Changeups have been the primary out pitch against OHB. As I mentioned earlier, they make up about 3x greater portion of the pitch mix against OHB than SHB. With that statistic, you’d probably guess that changeups enjoy a platoon advantage against OHB. However, that isn’t the case. SHB and OHB have very similar wOBA against changeups, .291 and .293 respectively. Changeups actually generate swinging strikes at a higher rate against SHB than OHB, 18% vs 15%. So why are changeups not more heavily used against SHB?
One reason is that sliders on average are a more effective pitch against SHB than changeups. Significantly more effective, .259 wOBA vs .293 wOBA even though both generate swinging strikes at the same rate (18%). It therefore makes sense to use a slider over a changeup against SHB. Case closed? Not so fast. There are a group of major league pitchers who have changeups that are more effective than their sliders. Logically you’d expect this sub-group of pitchers to use their superior changeups more frequently than their less effective slider, even against SHB. That’s not the case. I think there is some power to the tradition of slider to SHB, changeup to OHB mentality, whether or not it fits a specific pitcher’s abilities.
Here are three pitchers who could benefit from increased changeup usage to SHB.
Castillo has the second highest usage of a changeup against SHB of qualified starters in 2019, but with it’s effectiveness, he could stand to ride it even more. Greinke and Minor’s changeups aren’t as dynamic, but I think they’d benefit from a usage shift, perhaps equal slider and changeup usage rates vs SHB. Basically, my conclusion is that because changeups have no noticeable platoon advantage, they should be deployed in relation to the quality of the individual pitcher’s changeup. More like how guys with plus curveballs use the pitch heavily against both left and right-handed batters.