2025 is the year of the left-handed pitcher

Forty percent of the 2025 MLB season will be done by the end of this weekend, which is a big enough chunk to note this curious development: Left-handed pitching is enjoying unprecedented success.

It's not just that major-league hitters are producing their worst batting average (.234) versus lefties since 1886, or that left-handed pitching is enjoying its best K-BB% spread (14.7 percentage points) in the game's history entering play Friday, but southpaws are also enjoying their best wRC+ mark, which adjusts for ballpark and run environment.

Batters have produced a 93 wRC+ against lefties this season, the worst on record. The metric dates back to 2002. In each of the previous six seasons, wRC+ versus lefties ranged from 99-102.

Lefties are also enjoying their best collective ERA (3.61) since 1981.

What is going on?

One factor is the incredible number of ace-level left-handed pitchers.

Since 2002, left-handed pitchers have typically accounted for 25-29% of all plate appearances each season. This year, they're near the lower end at 25.9%.

Yet an unusual proportion of excellent starting pitching is left-handed this season: nine of the top 15 pitching fWAR leaders are lefties. Last season, it was five of the top 15.

But those aces combined account for just 15% of the total batters faced by left-handers, so there's more to it than a few pitchers having excellent seasons.

"I think over the years, lefties have gotten better compared to right-handed (pitchers), but it is gradual and noisy," one AL executive said.

For instance, left-handed fastball velocity has improved from 90.6 mph in 2008 to 93.4 mph this season. That's a greater rate of improvement than right-handers, whose four-seam velocity has risen from 92.4 mph in 2008 to 94.6 mph in 2025.

Teams are also taking a slightly less platoon-heavy approach with their hitters this season, putting lefty pitchers in a slightly more favorable position.

Left-handed hitters are facing left-handed pitchers in 30.4% of their plate appearances, which is the highest mark since 2012. If it held for the season, it would be the first time the rate has reached 30% since 2014. It's an increase of 2 full percentage points from 2024.

"The lesser platooning part is interesting and could play a role," another AL executive said. "I'll always bet on noise before anything else, but we should have a decent sample at this point, so maybe it's real."

David Cone, the longtime pitcher who is now a television analyst with ESPN and YES, believes the focus on certain types of pitch design might also favor lefties - especially against left-handed batters, who are hitting just .226 against southpaws.

"My eyes tell me that the pitch design is more east to west: two-seamers inside and sweepers away, especially two-seam inside to set the tone," Cone said. "It's very difficult for lefty hitters to hang in there and still cover inside fastballs."

Lefty sweeper and slider usage is at its highest point of the pitch-tracking era.

Sweepers and sliders make up 22.8% of all pitches thrown by lefties this season, a massive increase from the 2008-18 average of 13.3% and up a couple ticks from even 2024 (19.5%).

Lefties have always enjoyed a deception advantage simply because batters don't see them as often. But in the age of velocity-building throwing programs and pitch-design magic, they are closing the skills gap, too.

They are throwing harder with nastier breaking balls. Combine that with fewer platoons this season and a rare collection of left-handed aces, and 2025 just might be continue to be the year of the lefty.

Travis Sawchik is theScore's senior baseball writer.