Statcast has measured bat speed for two seasons now. Quickly becoming one of the most important additions to the public statistical record. But open the leaderboard, and the names at the top are the ones you would probably expect. Big, strong, and young. The 24-year-old, 6-foot-4, and 230-pounders. Not much of a surprise, just physics.
BSAx aims to ask a better question. Who swings hardest for their size and age?
BSAx stands for Bat Speed Above Expected. One number, in miles per hour.
Take a hitter's average bat speed on his competitive swings. Then set an expectation from three facts about the player: height, weight, and age. Subtract the expectation from what he actually did and what is left over is BSAx.
A positive BSAx means he swings harder than his size and age would predict. Negative means the reverse. A BSAx of plus-5 means a hitter swings five miles per hour faster than a typical player his size and age.
The expectation comes from a simple model. Feed it every qualified hitter's height, weight, and age, and it learns the league's going rate. Bigger and younger tend to swing harder. The model aims to draw the line through the middle of the league.
Size and age explain about a quarter of bat speed. That leaves the other three quarters on the table. BSAx helps explain some of that portion. The part of the swing that the tape measure and the birth certificate do not take into account.
Any new metric has to prove it measures the hitter rather than random variation. A BSAx that bounces around from season to season is just measuring noise rather than the hitter. But testing across Statcast's available data the correlation is strong (r = 0.88). A hitter who beats his frame one year tends to beat it the next. A repeatable trait and hurdle that BSAx clears.
A few honest limits, because they matter.
BSAx and raw bat speed agree about 80 percent of the time. This is not a hidden stat. It is a lens on an already public stat. If you want the hardest swingers in absolute terms, the Savant leaderboard already has them, and it is the industry's authority.
BSAx does not exactly match Baseball Savant hitter-for-hitter. Although MLB has publicly defined competitive swings, reproducing every published value requires the same swing-level bat-tracking dataset and processing pipeline that Savant uses. Using publicly available data, BSAx closely tracks Savant at the league level (r = 0.94). The league-wide signal is robust, but individual values should be viewed as close approximations rather than exact replicas.
Story One: Corbin Caroll
Corbin Carroll is listed at 5-foot-10, and 165 pounds. He swings the bat at 75.6 miles per hour. That is faster than a stack of hitters who outweigh him by sixty pounds.
Adjust for his frame and Carroll ranks among the top three swings in baseball. He is rarely the biggest hitter in the box. He is often the quickest to the ball. The raw leaderboard buries that under a wall of corner sluggers. BSAx brings it to the surface.
Story Two: Mike Yastrzemski
Mike Yastrzemski ranks around 210th in raw bat speed. On the naked leaderboard he looks slow. He is 35 years old and 180 pounds. Account for that, and his swing jumps to about 24th in the sport.
This is the clearest case for why the adjustment exists. Some hitters are not slow. They are small, or past their physical peak, or both. The raw number reads that profile as decline. BSAx reads it as a bat that still plays well above what the body should produce. A climb of roughly 185 spots once you control for age and frame is not a rounding error. It is a different, and fairer, way of seeing the same swing.
Story Three: The Age-defiers
Bat speed is supposed to fade with age. The aging curve is one of the most reliable things in the sport and these hitters are ignoring it.
Kyle Schwarber is 33 and swings 77.1 miles per hour. That is a top-five swing outright, before any adjustment, at an age when most bats have slowed. Matt Chapman, also 33, sits at 76.1. Mike Trout at 34 still rates as elite for his age. Byron Buxton at 32 also joins them.
Aging curves are averages, and averages are built out of exceptions. This is what a cluster of those exceptions looks like in one season. When a hitter this far along the calendar holds the bat this quick, it belongs on the record.
Story Four: No Adjustment Needed
Most of the names on the size-adjusted leaderboard are there because of the adjustment. Junior Caminero is there without it.
He is 22 years old. He leads baseball in raw bat speed at 80.0 miles per hour. He also leads it after adjusting for age and frame. He is the rare hitter who tops both lists, which tells you his swing is not a product of his size and not a product of his youth. It is simply the fastest one in the game, and he is at the very start of his career.
BSAx is a small idea, applied honestly. It takes a number you can already look up and asks who beats their own body with it. This season the answer is Corbin Carroll, a 35-year-old Yastrzemski, a group of veterans the aging curve has not caught, and a 22-year-old who needs no adjustment at all.
Data: 2026 season through early July, competitive swings only, qualified hitters. The season is in progress, so treat the smallest samples as a watch list. BSAx is a size-and-age adjustment on public Statcast bat-tracking data.
More from MKDC: the research section, the live PIX board, and the call-up model methodology. For the metrics behind the metrics, the handbook.