By Jon Becker

Every batter loves hitting home runs, and every pitcher hates giving them up. On the flip side, hitting a ball to the warning track or knowing you “just missed it” as a hitter is surely infuriating while inducing a sigh of relief on the mound. On the scoreboard and in the basic stat logs, home runs are home runs, and outs are outs. But, with the help of batted ball data, SIS is able to assign an expected value on each ball in play. 

This is similar to Statcast’s expected stats, though different inputs are used. Ours consider where the ball was hit and how far it was hit.

For example, let’s take an absolute no-doubt home run: a ball in play that, based on ball speed, trajectory and location, will always be a home run. Something like this Vladimir Guerrero Jr. home run. This is basically a home run anywhere. And since it actually was a home run, the difference between his actual home runs and his expected home runs for that at-bat was zero.

Then you get wall-scrapers, like this Jason Heyward home run from earlier this week. So, he hit one more home run than expected. If the expected home run value had been, say, 0.05, he would have hit 0.95 more home runs than expected.

If a player hit a well-struck ball that was caught at the warning track (or was any other result besides a home run) that had an expected home run value of 0.75, he would have hit 0.75 fewer home runs than expected for that plate appearance. So, to end up with a player’s season total, we add up their actual home run totals, and then subtract out their expected home run totals.

First, let’s take a look at who’s sneaking more balls over the fence than we think they should be:

PlayerTeamActual HRExpected HRDifference
Rhys HoskinsPhillies149.84.2
Alex BregmanAstros1813.94.1
Hunter PenceRangers1410.13.9
Jesse WinkerReds106.43.6
Clint FrazierYankees117.53.4
Gleyber TorresYankees1410.53.4

And now, some hitters who are hitting the ball well quite often but not getting to trot around the bases as much as we’d expect them to:

PlayerTeamActual HRExpected HRDifference
Adam JonesDiamondbacks1216.2-4.4
Brandon BeltGiants912.7-3.8
Josh BellPirates1922.7-3.7
Paul GoldschmidtCardinals1215.4-3.4
Joe PanikGiants35.9-2.8

When looking at the hitters’ names in isolation, there isn’t really much of a pattern as to who’s on the first table versus the second. Hoskins and Bregman are both well-known for raw power; so too are Goldschmidt and Donaldson. Winker isn’t exactly known for being a slugger; neither is Panik. But, when digging deeper, with plenty of help from video of the balls in play, we can see an obvious trend: the ballpark matters!

Take a look at this home run that Hoskins hit off of Diamondbacks closer Greg Holland earlier this week. Yes, it went 365 feet and went at least five rows into the stands, but it was just under 99 miles per hour off the bat; he clearly didn’t get all of it. It looked like a more impressive home run than it was because of the ballpark and hit location, but the reality of the matter is that it wouldn’t have even been a home run at every ballpark.

Now let’s watch a clip of Panik hitting a double. He hit that pretty well! In fact, it was just three miles per hour slower off the bat than Hoskins’ round-tripper. But, unfortunately for the Giants’ second baseman, his own home ballpark let him down.

Oracle Park is well-known for its jet stream knocking down fly balls, and if you look closely, you can see that those flags above the wall are indeed blowing in a bit. And, of course, there’s the height of the wall itself; at 25 feet, it’s the tallest right field wall in the majors. And so, despite a high expected home run value (higher than two of his three home runs this season), Panik had to settle for two bases.

There are so many variables that go into hitting a home run. Next time you see one sail just over the fence, ask yourself: how fortunate was the hitter to have hit that one?