Final yr, I took an extended take a look at the predictive energy of rookie exit velocity. One of many issues I realized was that for rookies with at the least 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 total efficiency by their complete rookie season. Exit velocity issues rather a lot, 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 eager 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 certainly 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 workforce 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 name. The remainder of us simply need to make do with rumors and innuendo suggesting that groups most frequently worth one thing akin to 90th-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 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 Number Munchers. After I bought eaten by a troggle, I organized the info in 3 ways. First, I basically did a longitudinal research. I needed to have a look at the large image and learn how effectively every methodology correlated with success after we had a number of knowledge. I mixed all three seasons price of knowledge, and bought a pattern of 398 gamers with at the least 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 at the least 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 at the least 30 within the following season, leaving me with 165 units.
Earlier than I inform you what I realized, right here’s a refresher in regards to the three statistical strategies for breaking down a participant’s exit velocity knowledge. You possible know most of this, however I believe it’ll be useful to have it in a single place.
Common Exit Velocity/Finest Pace
Common exit velocity has been with us because the starting of the Statcast period, and its primary draw is its simplicity and ubiquity. Nobody wants the idea of a mean defined to them, and you may search for 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 always ignore,” and calling it “the worst thing to rely on.”
Tango is a proponent of Finest Pace, which remains to be a mean. The distinction is that finest pace 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 virtually sure to finish up as outs, so why allow them to add pointless noise to the pattern? As Tango put it on his blog final yr, “The truth is that we be taught nothing a couple of batter on their gradual hit batted balls.” He revealed the chart beneath to indicate why he settled on 50% has the cutoff.
For every season with at the least 100 BBE, Tango calculated the correlation coefficient between finest pace 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 pace additionally tends to be sticky from yr to yr. There have been 1,080 circumstances the place a participant had at the least 100 tracked batted balls in two consecutive years, and people gamers have modified their finest pace by multiple commonplace deviation simply 6.6% of the time.
Finest pace was added to Baseball Savant final fall, however I believe 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. To be able to discover it, it’s a must to add it to your personal custom leaderboard.
Exit Velocity Percentiles
Exit velocity percentiles are similar to finest pace, however slightly than, say, giving us the typical of a participant’s high 50% hardest-hit balls, they only 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 a number of weeks digging by exit velocity knowledge in the hunt for 2023 breakout candidates. Particularly, he was centered on gamers with stable Ninety fifth-percentile exit velocity numbers however unimpressive average exit velocity numbers or contact rates. Since Ninety fifth-percentile exit velocity is an effective stand-in for uncooked energy, the thought was that the primary group would take off if they might lower down on mis-hits and the second group would accomplish that 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 manner. His second takeaway was that EV95’s usefulness comes largely as a result of this can be very sticky, even stickier than finest pace. With so little room for variance, you can’t fake 95EV.
Certainly, exit velocity changers are uncommon: solely 4% of hitters noticed their Ninety fifth-percentile exit velocities change by at the least one commonplace 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 at the least a normal deviation. It’s a loud statistic, in different phrases; you would possibly assume which you could inform the distinction between two hitters based mostly 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 commonplace deviation 4 instances as ceaselessly as they modify their top-end energy.
Over at Pitcher Record in 2021, Jeremy Siegel got here to the same conclusion relating to EV90, discovering it far 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.
Arduous-Hit Charge
Arduous-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 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 multiple commonplace deviation, the 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 perfect threshold for evaluating gamers. As you’ll see in a few of the graphs that observe, over an extended 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 pace at intervals of 5 share 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 also be their max exit velocity). I did the identical factor with finest pace, 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 also 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 measurement. It actually, actually issues. The much less info you have got, the extra it’s best to care in regards to the high finish of the size. Right here’s the correlation between wOBAcon and every of our three strategies over the course of our largest pattern.
Let’s bear in mind the rationale that exit velocity is so helpful. Like so many different new metrics that permit us take a look at issues extra granularly, the advantage of exit velocity is that it stabilizes far more rapidly than conventional stats. If now we have a number of years of knowledge for a hitter, their efficiency will communicate for itself and we received’t must 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 measurement.
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. Remember that within the graph above, after we mixed all three seasons price of knowledge and appeared solely at gamers with at the least 300 balls in play, the edge that was correlated most strongly with wOBAcon was EV74.
In a single-season pattern of at the least 100, the predictive energy peaks at EV81, nevertheless it’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 stable contact persistently is extraordinarily vital. However when there isn’t sufficient time to exhibit 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 finest pace.
The blue line seems pretty much like the graph that led Tom Tango to set finest pace at 50%. Actually, taking a look at wherever from the highest 35% to the highest 60% of batted balls would give us the same prediction for the subsequent yr. However for a shorter pattern, if we need 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 way messier, however the lesson is similar.
With a much bigger pattern, hard-hit price is most predictive when the cutoff is about at 101 mph, nevertheless it’s roughly as efficient wherever between 98 and 104 mph. With a smaller pattern, the edge 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 methodology is nearly equally helpful at predicting how profitable a participant will likely be once 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 search out them, one metric to carry all of them and in the dead of night bind them.
That mentioned, after digging into all of this knowledge, I believe that I personally will likely be more likely to make use of finest pace going ahead. The caveat I simply gave, “supplied you set your threshold on the proper stage,” issues fairly a bit, and finest pace’s threshold has bought essentially the most margin for error. For instance, take our longitudinal research. Right here’s how every methodology correlated to a participant’s ISO over a pattern of at the least 300 BIP.
All three metrics peak at r = .74, however take a look at how for much longer finest pace stays in that ballpark than percentile and hard-hit price. Percentile will not be far behind it, and taking a look at these graphs, I can see why groups have chosen EV90 or one thing near it. Arduous-hit price is far more finicky.
That segues into the second purpose that I plan on utilizing finest pace going ahead: it’s straightforward to search out. Since I’ll not often must recalculate it myself based mostly on the pattern measurement, I can simply pull it from Baseball Savant. If you wish to know a batter’s EV80, EV90 or EV95, you’ll possible 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 best to tug in the event you’re taking a look at a very small pattern measurement. In truth, right here’s a Baseball Savant search query ready to go with a threshold of 107 mph. Simply alter the dates to fit your wants.
One different good thing about finest pace 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 dangerous. I believe that ease of use is an especially underappreciated a part of in the present day’s superior stats, and having one other go-to metric that’s straightforward to grasp will make a giant 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. For those who don’t like that, how about hard-hit balls per pitch in the strike zone? Unsurprisingly, Corey Seager comes out on high there. As I mentioned originally, I’m certain that every one 30 groups have a report that appears roughly like this one, although maybe with fewer Lord of the Rings references. Finest pace and EV90 could not have been cast within the fires of Mount Doom, however they’ll get you a lot of the manner there.
