Testing Baseball Lore: Do Lefty Pitchers Have An Advantage?
As a lefty entering 9U Kid-Pitch, coaches made sure at a young age that I knew how to pitch. Lefty baseball players from all around the world will likely tell a similar story. It is ingrained in the fiber of most little league coaches, Major League Baseball fans, and even professionals… that lefty pitchers generally have an advantage when stepping onto the mound versus righty pitchers. It stands as another scroll in the large library of dogmatic baseball advice, with managers of all types using this knowledge consciously or subconsciously to influence their decisions. And while sometimes this dogmatic advice can be statistically true, the critical error comes in taking the knowledge at face value. Is there any actual truth to this lore? There have been multiple looks at a similar question, but the point of this article is to provide a more up-to-date look at the question, as well as a wider variety of surrounding points. In acknowledging all of these factors, one can digest the issue as a whole.
The Preface: Platoon Advantage
Before diving into this, there is a critical premise that needs to be re-established - the platoon advantage does exist. Most notably proven in The Book: Playing the Percentages in Baseball, it should be known that lefty pitchers have an advantage against lefty hitters, and righty pitchers have an advantage against righty hitters. When the pitcher faces the batter of the opposite handedness, the batter now has the comparative edge. And while this has been proven again and again in other pieces, it seems hypocritical to not provide the basic evidence of the premise in this piece. Using data from 2012-2022 (excluding 2020), these are the wOBAs for each hitter and pitcher handedness matchup weighed by the number of games in each season:
As is apparent in the table, Right-Handed Pitchers did about 15 points better against the same-handed hitter, and Left-Handed Pitchers did about 32 points better than the same-handed hitter. With this data being over a decent sample of years (10) and still being somewhat sizeable, it is very safe to again conclude that Tom Tango was right. With that etched in stone, the potential advantage or disadvantages of Lefties will be much easier to prove.
Handedness Pitcher Value As A Whole
Probably the most basic look of the whole article, showing the overall value of Lefties and Righties as a whole, regardless of matchup, can give a good sense of if one noticeably has a larger advantage. As a whole over the sample, Lefties' wOBA against is 0.315471, while Righties' wOBA against is 0.314833. Rounded to the nearest third decimal place as wOBA generally is calculated, they both stand equal at 0.315. Only the deeper look showcases the 0.638 points (0.000638) difference. Needless to say, this difference is negligible and shows no sign of a certain-handed pitcher having the advantage over the other. A similar story is told with OPS against, as both sides averaged 0.727. In regards to their ability to get outs themselves while limiting free passes (K% - (BB% + HBP%)), LHP’s total batter faced average was 12.2%, while RHP’s was 12.3%. This difference is again very minute.
As a whole, neither hand of pitcher does not have an advantage over the other based on the outcome. But what about on a year-to-year basis? Was there any given year where one hand absolutely outshined the other? Here is the wOBA of each hand, by year.
Only one year stands out on the graph - 2019. In 2019, Lefty pitchers allowed 6 more points of wOBA compared to Righties. In the grand scheme of baseball, those 6 points are very minute to be the max difference in a given year over a large sample of seasons. Hence, this is still not enough to prove using one would be more advantageous.
Handedness Pitcher Value By the Matchups
While touched on in the preface, a more in-depth look at the platoon's advantage and detriment for certain-handed pitchers can help analyze this lore more effectively. As can be seen in the matchup table above, same-handed matchups have a pitcher's advantage, while opposite-handed matchups curl towards the hitter. Though the fact of advantage remains constant, the actual degrees of these advantages are much different. Reiterating from above, Lefties did 32 points better against their same-handed opponents than their opposite-handed ones (0.293/0.325). Righties did only 15 points better (0.308/0.323). A 17-point difference is a relatively significant margin, and such exploitation of matchups could add up to lots of runs saved over a large enough sample. To put this into perspective, here is the year-over-year platoon advantage for lefty and righty pitchers.
For this graph, a positive platoon advantage (as shown) equals a lower wOBA allowed. Over the entirety of the sample, the Lefty wOBA platoon difference remains significantly higher, with the two lines not overlapping once. That spread was maximized in 2021 when LHPs were gaining 40 points off of the platoon compared to the RHPs’ 12 points. Against the opposite-handed batter, the two sides produced similar numbers, with RHP/LHH averaging a 0.323 wOBA and LHP/RHH averaging a 0.325 wOBA. Given that they’re both at a somewhat equal disadvantage, the potential matchup exploitability of a Lefty could prove a point regarding an extra sense of value.
Both of these points prove, to an extent, a sense of extra value for Lefty Pitchers. It showcases a point of exploitability for which certain special situations make them valuable. And while the aggregate statistics show no such difference, the optimization of these situations could ultimately prove to make Lefties more valuable as a whole in comparison to Righties. Of course, there are sure to be diminishing returns concerning this, which will be discussed further in one of the following sections.
Pitcher Stuff by Handedness
While this point has been iterated in many articles, such a look does not feel justified without it - Lefty Pitchers don’t have as good of stuff as righties. Using Savant pitch data solely from the 2022 season, these charts provide ample evidence of that:
Within the average velocities, Righties were the winners for every one of the major pitches used in the data. While some pitches were by wider margins than others, leading in every possible pitch shows that their ability to pitch at higher than lefty speeds is existent. The Spin rate story is a little less straightforward.
Of the 7 pitches that were looked at, RHPs led in spin in four - Sliders, 4-Seams, Sinkers, and Splitters. For the first five pitches shown, it is generally good to lead in spin, as it is slightly associated with increased pitch performance. For the last two (Changeups and Splitters), the pitches generally thrive in their ability to have limited spin. Even discounting those two, the Righties still hold a slight edge in their ability to generate spin in comparison to Lefties. Pitch shapes add another perspective to get a better overall view of each hand's "stuff".