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:

All Visuals by Kane Schwarz.

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".

As shown in the graph, each shape of each pitch is broken down by their Lefty and Righty locations. Within this comparison, the advantage is less obvious. The shapes are so similar between the two groups that surmising a clear advantage for one may be overstating the significance of the evidence. The only shape that seems obviously better than the other between the groups is the Sweeper. Lefties averaged roughly 2 more inches of horizontal break on these pitches, while the vertical break was somewhat similar. Sweepers typically thrive on their ability to "sweep" away from the batter, making the average Lefty sweeper arguably more effective than the average righty version. It is worth noting that the sample for these was decently smaller than the others, making a conclusion not as sound as it possibly should be. Within shape data, they're roughly on an even playing field.

Supply and Demand

It is well known that there are more righties in the world than lefties. According to one survey by BBC, only 10-12% of the population is estimated to be left-handed. Yet, Fangraphs pointed out that 29% of all Innings Pitched are thrown by a Left-Handed arm. Lefties manage to pitch 2.64x more than what their expected rate would be given the world population. Righties, on the other hand, pitch at roughly 0.81x their expected rate. But to be honest, even if one was not already aware of the exact numbers, they could’ve made such assumptions about lefties being overrepresented compared to expectations in the baseball world. After all, the age-going myth was that lefties were inherently better pitchers. But given that they are not except in special situations (which many organizations are likely aware of), then why does their population remain high?

For starters, roughly 30% of MLB hitters prefer to bat from the left side. This does not mean that they are necessarily lefty, as lots of right-handed throwers find that they are more effective at hitting from the left side, whereas the same generally does not apply in reverse. This 2009 Hardball Times article by Steve Treder article states that there have only been 57(!) from 1871-2009 (the minimum requirement is that the player played at least one-half game at a position other than pitcher). The number has undoubtedly grown in the years since this research was published, but it proves mostly lefty throwers generally stick to their side. With this, a divide is created - if selected from a random sample of people, more people are likely going to hit from the left side than throw from the left side. With the lefty-lefty matchup being so incredibly valuable to defense, it would justify the need for extra lefty pitchers to the extent of the population of left-handed hitters. This remains true in general, as having an advantage in such plate appearances can negate the disadvantage against right-handed hitters. As that is their only significant extra value, it can be consequently argued that having Lefty pitchers is only as useful as how many left-handed hitters are in the MLB population.

Since the population of lefty hitters naturally exceeds lefty pitchers, but such an equilibrium between the two can prove profitable for defense, lefty pitchers will generally be paid more relative to their stuff or ability to get outs. This was proven in this paper by Jarrett Korsen. And while the paper may have not used the preferred baseball statistics, it does show that the difference between Lefty and Righty pay is existent based on notable numbers. The only logical explanation for this is due to the lack of supply (relative to demand) and extra profitable utility previously mentioned. Such an alteration in the supply of Left-handed hitters would affect both utility (the amount of PAs where the platoon advantage is present) and demand (more/less left-handed pitchers are needed depending on the possibility of being able to utilize the platoon advantage). Keeping these factors in mind is important in considering the value structure behind a Left-handed Arm, and whether the advantage exists.

The Answer

While it has been touched on throughout the article, there still needs to be a clear declaration - based on the evidence, lefty pitchers are only extra valuable and have an advantage for their inherent handedness when they are facing a left-handed hitter. Besides, in that unique situation, all bets are off. When reviewing the performance from both sides as a whole, they yielded almost indifferent statistics in performance. After comparing their “stuff” or “skill”, the numbers suggest that lefty pitchers may be worse (on average) or barely equal to righties. And while they may be paid more due to their rarity in the market, an LHP’s true value is roughly equivalent to an RHP, provided they are not in the aforementioned situational matchup.

As stated, the common dogma is that Lefty pitchers generally have a bigger advantage on the mound than righties. From this evidence, it is fairly safe to conclude that this is false. While that advantage does exist in certain spots, as a whole, it is generally an untrue statement. Of course, there are always exceptions to the rule - certain teams may flail against left-handed pitching, but absolutely dominate righties, providing more of an advantage for a singular matchup. Certain teams may find lefties more advantageous to their overall roster, just due to the number of righties on their team and the need to diversify. But as a whole, it evens out. Given this, from an acquisition standpoint, it generally does not make sense to consider one pitcher better over the other solely due to their handedness.

Author’s Note:

While this is somewhat digging into the weeds, an argument could be made to prefer a left-handed pitcher over a right-handed pitcher, given that their skill metrics were even. To demonstrate this simply, let’s suppose two pitchers have about the same arsenal. All of their pitches are roughly the same, with an unmeaningful amount of variation in their “stuff”. Picking out a pitch, let’s suppose both of their sliders spin at 2600 rpm. Within their respective handedness percentiles, the lefty would be ranked higher, as the group generally carries a lower median for slider spin rate. And given that LHPs and RHPs produce roughly the same numbers with their respective skill metrics, then a higher ranking (from any category) would be preferred, as it’d produce better numbers relative to the handedness. Ergo, it would make sense to prefer the lefty in that situation.

As a whole, it would be better to reference their respective percentiles over their actual numbers, as the percentile scale for each produces the same amount of value on average. While their overall advantage/disadvantage may not be so different, differentiating between Lefty and Righty pitchers is a key part of considering skill comparison.