The reason left-handed hitters have decreased over 10 years in MLB
The shocking fact that the number of left-handed hitters in MLB has decreased by 5% over the past ten years
After the WBC, the 2023 MLB season will finally begin. The biggest news this offseason is that many players got big contracts. But even without any major signings, the Blue Jays’ offseason was good. They added Chris Bassitt and Erick Swanson to their above-average pitching staff. As for the fielders, they traded L. Gurriel and T. Hernandez, who had contributed to the team for the past few years. At the same time, they acquired D. Basho, B. Belt, and K. Kiermaier. News of the hitters moves all indicated that the intention was to fill the team’s shortage of left-handed hitters.
The Blue Jays were not, in fact, alone in their search for a left-hander. The Yankees were reportedly looking for a right-handed outfielder to replace the veteran, A. Hicks. New acquisitions have never occurred, but trade rumors will continue throughout the season.
One thing the Yankees and Blue Jays have in common is that the team’s lineup has a lot of right-handed batters. Last year, the Yankees had A. Rizzo (G. Gallo until mid-season), and the Blue Jays lineup had right-handed hitters except for C. Biggio.
These two teams are just examples of a few left-handed hitters on their batting orders. The Astros, who won the WS last year, have only K. Tucker, Y. Alvarez, and M. Brantley as left-handed hitters (and they were without Brantley for a long time last year).
Thus, left-handed hitters are fewer than right-handed hitters on many teams. But just as most people are right-handed, it is natural that most hitters are also right-handed. But here is a surprising fact. The number of left-handed hitters has been steadily declining over the past decade.
The graph below shows the ratio of left-handed batters to the total number of pitches thrown throughout a single season in MLB and the ratio of left-handed batters to the total number of at-bats yearly.
It is clear from this that the number of left-handed batters has indeed decreased beyond the margin of error; in 10 years, about 5% of left-handed batters have been replaced by right-handed ones. Most teams have 12–14 fielders, so a 5% change means that one or two hitters have changed from left-handed to right-handed batters. Since this trend is league-wide, it makes sense that the Blue Jays and Yankees have a shortage of left-handed hitters.
Why are there fewer left-handed hitters in MLB? In this article, I offer my hypothesis to this question.
Left-handed batters are struggling to hit right-handed pitchers
First, I looked at the wOBA of left-handed hitters against right-handed pitchers. I thought that some right-handed hitters called “lefty killers,” also get the opportunity against right-handed pitchers. So, they took the left-hander’s opportunity away from them.
The graph below shows the transition of wOBA for the entire league of wOBA last ten years by the pitcher and hitter pattern below.
(1) Right-handed pitcher vs. Right-handed batter (2) Right-handed pitcher vs. Left-handed batter
(3) Left-handed pitcher vs. Right-handed batter (4) Left-handed pitcher vs. Left-handed batter
Both left- and right-handed hitters have a 10-year up and down. Unlike right-handed hitters, however, left-handed hitters have seen a significant drop in performance since 2021. Left-handed hitters had the second-lowest wOBA vs. left-handed pitching in 22 years and the lowest wOBA vs. right-handed pitching in the last ten years.
This data shows that right-handed hitters taking a piece of the pie against right-handed pitchers is not necessarily true. Instead, it shows that the left-handed hitters gave up the pie by lowering their performance against right-handed pitchers rather than that the right-handed hitters took the pie.
We now know that left-handed hitters can no longer hit right-handed pitchers. So then, why are left-handed hitters unable to hit right-handed pitchers anymore? I thought about it.
Left-handed batters are unable to hit right-handed pitchers’ sinking balls.
For this reason, I examined the change in wOBA average of left-handed hitters versus right-handed pitchers by pitch type. This is because I wondered if the same thing that happened to left-hand hitters, where sinkers’ performance deteriorated throughout MLB due to the fly ball revolution, also happened to left-hand hitters.
Below are the changes in wOBA by pitch type for left-handed hitters vs. right-handed pitchers. First, here are the results by Fastball (4-seam sinker/cutter), Breaking (curve/slider), and Offspeed (changeup/split), which are the major categories of pitches on Baseball Savant.
wOBA against Offspeed dropped 25 points from a decade ago. And wOBA against Fastballs dropped little. But, Breaking balls, which have evolved significantly over the past few years, has stayed the same.
Let’s take a closer look at the pitches. In addition to Offspeed, I created the sinking pitch group( which includes Sinker, Changeup, and Split). The following graph shows the performance of the three pitches versus the other pitches (4-seam, cut, curve, and slider).
A clear trend emerged. The wOBA against sinker, changeup, and split have all deteriorated significantly since 2021, and last year were at their lowest levels in the past ten years.
Struggling against sinker, changeup, and split may apply to more than just left-handed hitters vs. right-handed pitchers, so I also laid out the other cases. The results are as follows. Even though there have been some up and down throughout the years, the left-hander vs. right-handed pitcher is worse than the other three patterns. In other words, it is a phenomenon peculiar to left-handed batters who play against right-handed pitchers that they have come to have difficulty with sinking balls.
The decline in wOBA of right-handed pitchers vs. left-handed batters is evident.
So far, we have found the answer to the question, “The number of left-handed batters has been steadily declining over the past decade.” The answer is that left-handed hitters struggle to compete with the sinking balls(Sinker, Changeup, Split) thrown by right-handed hitters. And this makes their opportunities in MLB decrease.
Why Left-Handed Hitters Cannot Counter Right-Handed Pitchers’ Sinking Balls
I also considered why left-handed hitters are struggling to compete with sinking balls thrown by right-handed pitchers. It is because the usage of the sinker has changed.
Specifically, the sinker has become more of a strikeout pitch rather than a ground ball. Various trends in MLB over the past ten years are related to this change.
First is the fly ball revolution. This has made hitters more inclined toward an upper swing. And sinker has become easy prey for hitters. The countermeasure to this sinker extinction crisis is the seam shift wake. The spread of this concept has led to an increase in the number of pitchers who throw sinkers with a bigger vertical move.
Some pitchers have begun to combine this new sinker with the changeup. For example, S. Alcantara, who won the Cy Young Award last year, uses this pitching technique as one of his weapons. From the batter’s point of view, it is tough to deal with a sinker close to 100 mph and a fast changeup in the 90 mph range on a similar trajectory.
Furthermore, left-handed hitters see these two types of pitches on the outside corner of the plate. The fact that the ball seems to be moving away from them makes it even more difficult for them to attack it(It is like Sweeper for the right-handed hitters).
The graph below shows the change in the sinker’s ground ball and strikeout rates. The strikeout rate has indeed gone up, while the ground ball rate has gone down.
The graph below shows the change in sinker’s GB% and K%. Indeed, the GB% has gone down, and the K% has gone up.
The sinker has gone from a pitch that only ground balls to a pitch that strikes out swinging strikes.
In other words, the evolution of the sinker has created a synergistic effect with the changeup. And it dominates left-handed hitters.
The left-hander has been on a steady decline over the past decade, particularly since 2021. 2021 is consistent with when the concept of the seam shift wake became widely popular among baseball fans.
Finally
The flyball revolution was born just about ten years ago. The trend gave hitters a significant advantage against sinker. But then the sinker made a comeback with the seam-shifting wake. It is on the verge of banishing left-handed hitters from the MLB stage (although it is unlikely that left-handed hitters will ever disappear). Some say that baseball is a perpetual game of weasel words between hitters and pitchers, and this 10-year war over the sinker may be the latest example.
Photo BY: Ian D’Andrea
