Final yr, I took a protracted have 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. Realizing only one measurement, the rate of a participant’s hardest-hit ball, was extra helpful than realizing about their total efficiency by means of their complete rookie season. Exit velocity issues so much, as does the way you interpret the info.
Because the rollout of Statcast in 2015, we’ve been launched to a few normal methods of enthusiastic 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 considered one of these strategies is most helpful. May there be one exit velocity metric to rule all of them?
I’ve to think about that in some unspecified time in the future within the final a number of years, the R&D division of every main league staff has requested itself that very same query. In every large league metropolis, somebody a lot smarter than I’m did the maths 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 need to make do with rumors and innuendo suggesting that groups most frequently worth one thing akin to Ninetieth-percentile exit velocity. To my information, nobody within the public sphere has made a complete survey, and I wished 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 good friend Mike to tug the batted ball knowledge (as a result of I felt fairly certain I’d screwed one thing up alongside the way in which) and crunched these numbers too. Then I finished to play Quantity Munchers. After I obtained eaten by a troggle, I organized the info in 3 ways. First, I primarily did a longitudinal research. I wished to have a look at the large image and learn the way properly every technique correlated with success after we had numerous knowledge. I mixed all three seasons value of information, and obtained 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 wished to verify how the metrics dealt with very small samples, so I targeted 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 probably know most of this, however I feel it’ll be useful to have it in a single place.
Common Exit Velocity/Finest Pace
Common exit velocity has been with us for the reason that 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 will not be a fan, saying common exit velocity is “a stat I at all times ignore,” and calling it “the worst factor to depend on.”
Tango is a proponent of Finest Pace, which remains to be a median. The distinction is that finest velocity types 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 fact is that we be taught nothing a couple of batter on their gradual 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 finest velocity and wOBAcon within the following season. Along with being a pleasant, spherical quantity, 50% is the place it turned most predictive of success on balls in play.
Finest 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 finest velocity by a couple of normal deviation simply 6.6% of the time.
Finest velocity was added to Baseball Savant final fall, however I think most individuals don’t even realize 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 personal customized leaderboard.
Exit Velocity Percentiles
Exit velocity percentiles are similar to finest velocity, however relatively 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 looking for 2023 breakout candidates. Particularly, he was targeted on gamers with stable 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 thought was that the primary group would take off if they may lower down on mis-hits and the second group would achieve this in the event that they lower 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 must always all begin referring to EV percentiles that method. His second takeaway was that EV95’s usefulness comes largely as a result of this can be very sticky, even stickier than finest velocity. With so little room for variance, you’ll be able to’t pretend 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.
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 typical deviation. It’s a loud statistic, in different phrases; you would possibly assume which you can inform the distinction between two hitters based mostly on their common exit velocities, however there’s an honest likelihood that you simply’re being deceived by variance. Hitters change their common exit velocities by an entire normal deviation 4 occasions as incessantly as they alter their top-end energy.
Over at Pitcher Record in 2021, Jeremy Siegel got here to an identical conclusion concerning EV90, discovering it way more secure 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.
Exhausting-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 sweet. 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 typically 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 a couple of 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 the most effective threshold for evaluating gamers. As you’ll see in among the graphs that observe, over a protracted pattern, the edge 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. Bear in mind how Tom Tango calculated finest 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 finest 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 house the significance of pattern dimension. It actually, actually issues. The much less info you could have, the extra you must 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 keep in mind the explanation that exit velocity is so helpful. Like so many different new metrics that enable us have a look at issues extra granularly, the good thing about exit velocity is that it stabilizes way more rapidly than conventional stats. If we now have a number of years of information for a hitter, their efficiency will converse for itself and we gained’t must verify their exit velocity fairly often. We’ll care about it when issues begin to change, so we’ll be a smaller pattern dimension.
With that in thoughts, check out the graph beneath. It reveals the correlation between exit velocity percentile in a single season and wOBAcon within the following season. Needless to say within the graph above, after we mixed all three seasons value of information and seemed solely at gamers with a minimum of 300 balls in play, the edge 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, however it’s roughly as dependable anyplace 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 far smaller, solely from EV94 to EV98. Over the long term, the flexibility to make stable contact constantly is extraordinarily vital. However when there isn’t sufficient time to exhibit consistency, success is most strongly correlated with the flexibility to actually crush the ball. The distinction is much more stark if we have a look at finest velocity.
The blue line seems pretty just like the graph that led Tom Tango to set finest velocity at 50%. Actually, anyplace from the highest 35% to the highest 60% of batted balls would give us an identical prediction for the subsequent yr. However for a shorter pattern, if we wish to predict how a participant will do subsequent yr, we must 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 far messier, however the lesson is similar.
With an even bigger pattern, hard-hit price is most predictive when the cutoff is ready at 101 mph, however it’s roughly as efficient anyplace between 98 and 104 mph. With a smaller pattern, the edge must be set at 107 mph.
You won’t have observed 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 will likely be after they put the ball in play subsequent season (in addition to predicting their total 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 carry all of them and at nighttime bind them.
That stated, after digging into all of this knowledge, I feel that I personally will likely be more likely to make use of finest velocity going ahead. The caveat I simply gave, “supplied you set your threshold on the proper stage,” issues fairly a bit, and finest velocity’s threshold has obtained probably 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 have a look at how for much longer finest velocity stays in that ballpark than percentile and hard-hit price. Percentile will not be far behind it, and these graphs, I can see why groups have chosen EV90 or one thing near it. Exhausting-hit price is way more finicky.
That segues into the second cause that I plan on utilizing finest velocity going ahead: it’s straightforward to seek out. Since I’ll not often must recalculate it myself based mostly 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 probably want to tug the info and calculate it your self, and that may be a ache. Regardless of being finicky, hard-hit price is the simplest to tug should you’re a very small pattern dimension. In reality, right here’s a Baseball Savant search question able to go with a threshold of 107 mph. Simply regulate the dates to fit your wants.
One different good thing about finest 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 larger is sweet, 99 or decrease is unhealthy. I feel that ease of use is an especially underappreciated a part of as we speak’s superior stats, and having one other go-to metric that’s straightforward to grasp will make an enormous distinction.
There are at all times going to be new methods to consider common exit velocity. Two years in the past, Ben Clemens got here up with the thought of hard-hit balls per swing. When 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 in the beginning, 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. Finest velocity and EV90 might not have been cast within the fires of Mount Doom, however they’ll get you a lot of the method there.