# The Balls Keep On Flying

Earlier this week Alex Gordon hit a home run. Okay, sorry, that’s a mean joke. I am referring to the MLB single season home run record, of course. There have been more home runs hit this season than in any season in Major League Baseball history. Whether this is a good or bad thing is a matter of debate. I’ve heard from many people who are unhappy with this turn of events, others who are quite pleased, and a small minority who have no strong opinion on the matter. That third group seems to be rather small, but that’s the way of things these days.

It appears that this home run record has been spurred on by artificial means, namely an apparent change to the ball. The exact change is difficult to pin down, unfortunately. On some level it deals with the flight characteristics of the ball, though. What some call the coefficient of drag. Essentially, the air isn’t slowing down the ball as much as before. There are conflicting reports as to why this might be the case. Some say the radius of the ball is smaller. Others say the seams are smaller. Maybe both are true, maybe neither. Maybe there are other variables. It is all very much up in the air at this point. But, we do know that the ball is flying ever so slightly further now, in 2017, than it was in, say, 2015. Or 2014. Or 2013.

Perhaps counter-intuitively, very small changes in flight distance can make rather large differences in home run rate. Perhaps more intuitively, differences in flight distance can be represented as changes in effective velocity.

This section of wall was moved in about 11 feet. The purple dots depict balls that would have been home runs over the original fence, while the blue dots depict only those that are home runs over the newer, shorter wall. Bringing in the fences 11 feet increased the home run rate by nearly 60%.

As it turns out, about 0.2 mph is roughly equal to one foot of flyball distance. Given that flyballs travel roughly 5 feet further now than they have in the past, accounting for all other variables, then we can say batted balls have an effective velocity roughly 1 mph greater than in the past.

This doesn’t mean the actual velocity is higher, mind you. In fact, it isn’t. Velocity is down this year from 2015, dropping from 87.1 to 86.6 mph, when you factor in various measurement errors, game time temperature, etc.

Since this boost in home run rate is rather artificial, and subject to the whims of a manufacturing process, these extra home runs are difficult to plan around. Will the home run rate remain steady going into 2018? Will the ball revert? Will MLB slowly phase out these changes in favor of the old ball? Maybe MLB will continue to heighten the effects of this new ball and increase home run rate even further. It is difficult to forecast the future, but there is value in understanding which players may or may not be getting helped by the current ball situation.

In order examine this question, I am using the algorithms I wrote for xStats to evaluate each batted ball. These algorithms first clean the available data from potential measurement errors, apply temperature and park adjustments, then group similarly hit balls to find their average success rates. After this, ball park effects are carefully applied, along with batter foot speed adjustments. Although in this case foot speed isn’t particularly important, since we’re only talking about home runs.

Rather than using the raw, measured exit velocity directly from Statcast for each batted ball, I am first subtracting 1mph to account for the change in effective velocity. I have gone through and calculated the impact of this effective velocity for each batter in MLB. Needless to say, some batters have gained very little, while others have gained a great deal. I want to highlight the players who have the greatest risk going forward.

### The 20 HR Guy

This season has a ludicrous number of guys with 20 or more home runs. I believe it is a single season record. Either way, there are a tremendous number of these batters, to the point where it is going to heavily dilute the value of power going forward. Both on the free agent market (which makes me believe the MLBPA will fight to get rid of this juiced ball) and in fantasy drafts.

When I subtract the effective velocity from the batters, the total number of batters with more than 20 home runs drops from 110 to 58. (note, these numbers are as of the morning of 9/20). Sorting by the fraction of home runs lost from their total, the highest risk batters in this group are:

From 20+ HR to < 20 xHR
Name HR xHR ΔHR % Change
Didi Gregorius 24 10.9 13.1 54.6%
Brett Gardner 20 10.8 9.2 46.0%
Luis Valbuena 21 11.9 9.1 43.3%
Matt Olson 23 13.3 9.7 42.2%
Zack Cozart 23 14.4 8.6 37.4%
Paul DeJong 23 14.5 8.5 37.0%
Marwin Gonzalez 22 13.9 8.1 36.8%
Jose Ramirez 27 17.7 9.3 34.4%
Ian Kinsler 20 13.3 6.7 33.5%
Scooter Gennett 26 17.5 8.5 32.7%
Elvis Andrus 20 13.5 6.5 32.5%
Albert Pujols 22 14.9 7.1 32.3%
Yasmani Grandal 20 13.6 6.4 32.0%
Javier Baez 22 15.0 7.0 31.8%
Ryon Healy 25 17.4 7.6 30.4%
xHR are estimated home runs given a drop in effective velocity.

Of everyone on this list, Jose Ramirez is certainly the most interesting. Especially after this breakout season in which he became one of the most valuable players in fantasy baseball. His power numbers this season are up considerably from his career highs, in 2016 he hit only 11 home runs, and prior to this season he had 19 total.

Ramirez is not a high exit velocity batter, hitting the ball only 87 mph on average, so the 1mph gain in effective velocity appears to be giving him just enough of a bump to push him from a low power guy up to a strong power hitter. While sacrificing nothing in terms of batting average or on base percentage.

Jose Ramirez appears to be hitting the ball into the air a bit more, raising a few ground balls to fly balls, while keeping the line drive rates steady. So that is one area of improvement. Perhaps this is driven by a reduction in out of zone contact rate. But his exit velocity has held steady. You’d expect it to increase with a reduction of out of zone contact.

Didi Gregorius and Brett Gardner are both at the top of this list, but don’t think it is purely due to Yankee Stadium park effects. There are Yankees all over the spectrum, and in fact Aaron Judge has among the lowest drops in expected home run rate after subtracting the 1mph effective velocity.

Didi Gregorius has popped up on just about every ‘overachieving’ list of players I have put together using Statcast data over the past two seasons. By every metric I have, his power numbers appear to be unsustainable. And yet he has sustained them. Could it be the ball? Perhaps. Perhaps he’s just an outlier. I’m not entirely sure.

All in all, this list is largely composed of breakout players, which likely scratches an itch for many people. Otherwise known as the “Scooter Gennett hit 4 homers in one game, something has gone wrong” club. Marwin Gonzalez, Paul DeJong, Scooter Gennett, Jose Ramirez. Nobody predicted these guys would have the seasons they have had. It does appear it was largely spurred on by the ball.

Although, even after accounting for the influence of the ball, the home run totals may still surprise you. It goes to show, not everything about this uptick in home runs is artificial. There are real mechanical changes and adjustments being made by players. Even if Jose Ramirez dropped down to 18 home runs to date, it would be a career high and he’d be on pace for doubling his single season home run total.

### The 10 HR Guy

Hitting 20 home runs is now commonplace, but the 10-15 home run guys are important, too. Here is a list of guys who drop below the 10 home run threshold when I subtract the effective velocity increase. There are 59 total batters in this group, but here are the fifteen who lost the greatest fraction of their home run total.

From 10+ HR to < 10 xHR
Name HR xHR ΔHR % Change
Kevin Kiermaier 14 6.3 7.7 55.0%
Max Kepler 18 8.6 9.4 52.2%
Eduardo Nunez 12 5.9 6.1 50.8%
Jose Reyes 14 7.3 6.7 47.9%
Orlando Arcia 14 7.6 6.4 45.7%
Manuel Margot 13 7.1 5.9 45.4%
Melky Cabrera 17 9.4 7.6 44.7%
Ender Inciarte 11 6.1 4.9 44.5%
Jordy Mercer 14 7.8 6.2 44.3%
Adrian Beltre 16 9.1 6.9 43.1%
Nick Williams 10 5.7 4.3 43.0%
Gregory Polanco 10 5.8 4.2 42.0%
Denard Span 11 6.4 4.6 41.8%
Pat Valaika 12 7.0 5.0 41.7%
Kurt Suzuki 15 9.0 6.0 40.0%
xHR are estimated home runs given a drop in effective velocity.

Max Kepler and Melky Cabrera stick out to me on this list. Both are nearly to the 20 home run mark, but could each fall below the 10 mark without the effective velocity. These home run differences all show just how much the effective velocity is helping these lower tier power hitters. Nearly half, and in some cases more than half, of the home runs they have hit this season were aided by an artificial boost in effective velocity.

These are the sorts of players that seem to stick in the craw of many baseball fans these days. The eye rolls as you see what was once a routine flyball on the warning track just barely clear the fence. Those extra five feet can make all the difference in the world.

Some of these guys likely will not remain low tier power threats forever. Nick Williams, for example. I believe he will develop more power as he ages and adjusts to the major leagues. You can see this maturation process over the past few weeks alone. Of course, you should never trust September numbers, but he is a good talent. Manual Margot is another such player, although I don’t think he will develop as much power as Williams.

### Home Run Totals

After subtracting the effective velocity, I have 4529 home runs on the season, down from the 5704 registered in game. Far from a record breaking pace, and actually a step down from the home run totals we saw in 2015. There are a few guys towards the top of the home run leaderboards which lost very few home runs from this exercise: Aaron Judge, Joey Gallo, Joey Votto, Manny Machado, Adam Duvall, and Francisco Lindor to name a few.

There are a few at the top of the leaderboard who lost a large number of home runs: Giancarlo Stanton, JD Martinez, Justin Smoak, Edwin Encarnacion, Khris Davis, and Cody BellingerThe average batter lost 20% of his home run total after removing this effective velocity.

Keep in mind that the Diamondbacks are contemplating running an experiment of their own in Chase Field next season if and when they install a Humidor. If that is installed, they could lose 25 to 50 percent of their home run total. So, in other words, it would not only reverse this boost in home run rate seen around the league, but it could go equally as far in the other direction. Perhaps dropping the pre-juiced ball era home run rates in Chase Field by 15 to 20%. I hope that puts the effects of the Humidor into perspective.

If you would like to view the complete list of batters this season, along with the differences in singles, doubles, triples, and hit totals click here.

Andrew Perpetua is the creator of CitiFieldHR.com and xStats.org, and plays around with Statcast data for fun. Follow him on Twitter @AndrewPerpetua.