Final yr, I took a protracted take a look at the predictive energy of rookie exit velocity. One of many issues I discovered was that for rookies with a minimum of 200 balls in play, wRC+ was much less predictive of their future efficiency than max exit velocity. That blew my thoughts. Understanding only one measurement, the rate of a participant’s hardest-hit ball, was extra helpful than understanding about their general efficiency by means of their complete rookie season. Exit velocity issues rather a lot, as does the way you interpret the information.
Because the rollout of Statcast in 2015, we’ve been launched to 3 basic methods of excited about exit velocity, together with half a dozen particular person variations. Relying on the context, we’d examine a participant’s common exit velocity, their most exit velocity, their hard-hit price, or any variety of exit velocity percentiles. For some time now, I’ve been questioning which one in every of these strategies is most helpful. May there be one exit velocity metric to rule all of them?
I’ve to think about that sooner or later within the final a number of years, the R&D division of every main league group has requested itself that very same query. In every massive league metropolis, somebody a lot smarter than I’m did the mathematics and wrote up the leads to a report that now rests comfortably in a proprietary database with a catchy title. The remainder of us simply must make do with rumors and innuendo suggesting that groups most frequently worth one thing akin to Ninetieth-percentile exit velocity. To my data, nobody within the public sphere has made a complete survey, and I needed to look into the matter for myself.
I pulled the exit velocity for each batted ball hit in the course of the 2021, 2022, and 2023 seasons and crunched the numbers. Then I requested my pal Mike to drag the batted ball knowledge (as a result of I felt fairly certain I’d screwed one thing up alongside the best way) and crunched these numbers too. Then I ended to play Quantity Munchers. After I bought eaten by a troggle, I organized the information in 3 ways. First, I primarily did a longitudinal research. I needed to have a look at the massive image and learn how effectively every technique correlated with success once we had plenty of knowledge. I mixed all three seasons value of information, and bought a pattern of 398 gamers with a minimum of 300 tracked balls in play.
Subsequent, I broke issues down by season to trace year-over-year modifications. I ended up with 610 units of back-to-back participant seasons with a minimum of 100 tracked balls in play. Lastly, I needed to test how the metrics dealt with very small samples, so I centered solely on gamers who had between 30 and 110 balls in play in a single season, after which a minimum of 30 within the following season, leaving me with 165 units.
Earlier than I let you know what I discovered, right here’s a refresher in regards to the three statistical strategies for breaking down a participant’s exit velocity knowledge. You doubtless know most of this, however I believe it’ll be useful to have it in a single place.
Common Exit Velocity/Greatest Velocity
Common exit velocity has been with us because the starting of the Statcast period, and its fundamental draw is its simplicity and ubiquity. Nobody wants the idea of a median defined to them, and you’ll lookup any participant’s EV proper right here at FanGraphs. It’s additionally very simply improved upon. Baseball Savant’s personal Tom Tango shouldn’t be a fan, saying common exit velocity is “a stat I all the time ignore,” and calling it “the worst factor to depend on.”
Tango is a proponent of Greatest Velocity, which continues to be a median. The distinction is that greatest velocity kinds a participant’s batted balls by exit velocity, throws out the weakest half, and takes the typical of solely the remaining, hardest-hit half. A ball hit at 40 mph and one hit at 60 are each nearly sure to finish up as outs, so why allow them to add pointless noise to the pattern? As Tango put it on his weblog final yr, “The truth is that we be taught nothing a couple of batter on their sluggish hit batted balls.” He printed the chart beneath to indicate why he settled on 50% has the cutoff.
For every season with a minimum of 100 BBE, Tango calculated the correlation coefficient between greatest velocity and wOBAcon within the following season. Along with being a pleasant, spherical quantity, 50% is the place it grew to become most predictive of success on balls in play.
Greatest velocity additionally tends to be sticky from yr to yr. There have been 1,080 instances the place a participant had a minimum of 100 tracked batted balls in two consecutive years, and people gamers have modified their greatest velocity by multiple normal deviation simply 6.6% of the time.
Greatest velocity was added to Baseball Savant final fall, however I think most individuals don’t even comprehend it’s there. It was launched with none fanfare, and it’s not on the participant pages or exit velocity leaderboard. With the intention to discover it, you need to add it to your individual customized leaderboard.
Exit Velocity Percentiles
Exit velocity percentiles are similar to greatest velocity, however somewhat than, say, giving us the typical of a participant’s prime 50% hardest-hit balls, they simply give us the precise exit velocity of their Fiftieth-percentile hard-hit ball. It’s simply the exit velocity of that one batted ball.
Again at first of the yr, Ben Clemens spent just a few weeks digging by means of exit velocity knowledge in the hunt for 2023 breakout candidates. Particularly, he was centered on gamers with strong Ninety fifth-percentile exit velocity numbers however unimpressive common exit velocity numbers or contact charges. Since Ninety fifth-percentile exit velocity is an efficient stand-in for uncooked energy, the concept was that the primary group would take off if they might minimize down on mis-hits and the second group would achieve this in the event that they minimize down on whiffs.
Ben hit on two vital issues: First, he referred to the measure as EV95, which is a lot extra concise that we should always all begin referring to EV percentiles that approach. His second takeaway was that EV95’s usefulness comes largely as a result of this can be very sticky, even stickier than greatest velocity. With so little room for variance, you may’t faux 95EV.
Certainly, exit velocity changers are uncommon: solely 4% of hitters noticed their Ninety fifth-percentile exit velocities change by a minimum of one normal deviation from one yr to the subsequent.
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If you wish to know why analysts focus extra on top-end energy than common exit velocity, right here it’s in a nutshell. In a given yr, 15.8% of batters see their common exit velocity enhance or decline by a minimum of a regular deviation. It’s a loud statistic, in different phrases; you would possibly suppose you could inform the distinction between two hitters primarily based on their common exit velocities, however there’s a good likelihood that you simply’re being deceived by variance. Hitters change their common exit velocities by an entire normal deviation 4 occasions as continuously as they modify their top-end energy.
Over at Pitcher Record in 2021, Jeremy Siegel got here to an analogous conclusion concerning EV90, discovering it rather more steady than the tenth, twenty fifth, Fiftieth, and seventy fifth percentiles, and noting that it was extra predictive of the next season’s efficiency than common exit velocity or hard-hit price. Chris Clegg has additionally argued that EV80 is extra helpful in predicting a participant’s future efficiency.
Laborious-Hit Fee
Laborious-hit price is one other stat that’s helpful due to its simplicity. Something hit over 95 mph is hard-hit, and hitting the ball exhausting is nice. This graph from the MLB.com glossary makes an eloquent case for 95 mph because the cutoff.
Fairly merely, that’s the spherical quantity the place efficiency begins to take off. Nonetheless, hard-hit price has usually been the worst of the three exit velocity strategies when it comes to predicting future offensive efficiency. Once I analyzed year-over-year modifications, 10.9% of gamers raised or elevated their hard-hit price by multiple normal deviation, the very best of all three strategies. Additional, whereas 95 mph is the place efficiency begins to take off on batted balls as an entire, it’s not one of the best threshold for evaluating gamers. As you’ll see in a few of the graphs that comply with, over a protracted pattern, the brink that’s most predictive of success for a person participant is nearer to 101 mph.
So these are the three strategies. I made a decision to be excruciatingly thorough. Keep in mind how Tom Tango calculated greatest velocity at intervals of 5 proportion factors? I calculated every metric one integer a time. That’s to say, I calculated every participant’s EV1, then their EV2, then their EV3, and so forth as much as EV100 (which can be their max exit velocity). I did the identical factor with greatest velocity, calculating the typical exit velocity of their hardest-hit 1% of batted balls, then the highest 2%, and so forth as much as 100% (which can be their common exit velocity). Lastly, I calculated their hard-hit price 1 mph at a time, calculating the proportion of balls over 1 mph, then 2 mph, and so forth. The hard-hit knowledge was solely helpful between 9 mph and 122 mph, in order that left me with 314 methods of analyzing every participant’s exit velocity. Then I calculated correlation coefficients between these 314 units of numbers and every participant’s wOBA, wOBAcon, and ISO.
This train actually drove dwelling the significance of pattern dimension. It actually, actually issues. The much less info you have got, the extra it is best to care in regards to the prime finish of the dimensions. Right here’s the correlation between wOBAcon and every of our three strategies over the course of our greatest pattern.
Let’s bear in mind the explanation that exit velocity is so helpful. Like so many different new metrics that enable us take a look at issues extra granularly, the advantage of exit velocity is that it stabilizes rather more rapidly than conventional stats. If we’ve got a number of years of information for a hitter, their efficiency will converse for itself and we gained’t have to test their exit velocity fairly often. We’ll care about it when issues begin to change, so we’ll be taking a look at a smaller pattern dimension.
With that in thoughts, check out the graph beneath. It exhibits the correlation between exit velocity percentile in a single season and wOBAcon within the following season. Needless to say within the graph above, once we mixed all three seasons value of information and appeared solely at gamers with a minimum of 300 balls in play, the brink that was correlated most strongly with wOBAcon was EV74.
In a single-season pattern of a minimum of 100, the predictive energy peaks at EV81, but it surely’s roughly as dependable wherever from EV70 to EV90. But when the participant has a smaller variety of balls in play, predictive energy peaks at EV96, and the reliability window is way smaller, solely from EV94 to EV98. Over the long term, the flexibility to make strong contact constantly is extraordinarily vital. However when there isn’t sufficient time to display consistency, success is most strongly correlated with the flexibility to essentially crush the ball. The distinction is much more stark if we take a look at greatest velocity.
The blue line seems pretty just like the graph that led Tom Tango to set greatest velocity at 50%. Actually, taking a look at wherever from the highest 35% to the highest 60% of batted balls would give us an analogous prediction for the subsequent yr. However for a shorter pattern, if we need to predict how a participant will do subsequent yr, we should always discard 92% of their pattern and look solely on the common exit velocity of the hardest-hit 8% of their balls in play.
The hard-hit price graph is way messier, however the lesson is similar.
With an even bigger pattern, hard-hit price is most predictive when the cutoff is about at 101 mph, but it surely’s roughly as efficient wherever between 98 and 104 mph. With a smaller pattern, the brink must be set at 107 mph.
You may not have seen it, however in all three of the earlier graphs, the blue line topped out at both .54 or .55. At its peak, every technique is nearly equally helpful at predicting how profitable a participant can be after they put the ball in play subsequent season (in addition to predicting their general wOBA and their ISO). Offered you set your threshold on the proper stage, none of those three strategies stands head and shoulders above the others. There is no such thing as a one metric to seek out them, one metric to deliver all of them and at nighttime bind them.
That stated, after digging into all of this knowledge, I believe that I personally can be more likely to make use of greatest velocity going ahead. The caveat I simply gave, “supplied you set your threshold on the proper stage,” issues fairly a bit, and greatest velocity’s threshold has bought essentially the most margin for error. For instance, take our longitudinal research. Right here’s how every technique correlated to a participant’s ISO over a pattern of a minimum of 300 BIP.
All three metrics peak at r = .74, however take a look at how for much longer greatest velocity stays in that ballpark than percentile and hard-hit price. Percentile shouldn’t be far behind it, and taking a look at these graphs, I can see why groups have chosen EV90 or one thing near it. Laborious-hit price is rather more finicky.
That segues into the second purpose that I plan on utilizing greatest velocity going ahead: it’s straightforward to seek out. Since I’ll not often have to recalculate it myself primarily based on the pattern dimension, I can simply pull it from Baseball Savant. If you wish to know a batter’s EV80, EV90 or EV95, you’ll doubtless want to drag the information and calculate it your self, and that may be a ache. Regardless of being finicky, hard-hit price is the simplest to drag if you happen to’re taking a look at a very small pattern dimension. The truth is, right here’s a Baseball Savant search question able to go with a threshold of 107 mph. Simply modify the dates to fit your wants.
One different good thing about greatest velocity is that in any season, the typical amongst certified batters tends to be proper round 99.7. That makes interpretation fairly easy: 100 or increased is nice, 99 or decrease is unhealthy. I believe that ease of use is an especially underappreciated a part of at this time’s superior stats, and having one other go-to metric that’s straightforward to know will make a giant distinction.
There are all the time going to be new methods to consider common exit velocity. Two years in the past, Ben Clemens got here up with the concept of hard-hit balls per swing. In the event you don’t like that, how about hard-hit balls per pitch within the strike zone? Unsurprisingly, Corey Seager comes out on prime there. As I stated at first, I’m certain that each one 30 groups have a report that appears roughly like this one, although maybe with fewer Lord of the Rings references. Greatest velocity and EV90 might not have been solid within the fires of Mount Doom, however they’ll get you a lot of the approach there.