Three Up, Three Down: Home Run Outliers to Buy or Sell

Jon Anderson identifies players who have been underachieving or overperforming on their expected home run rates to buy or sell in the fantasy baseball trade market for 2021 based on Statcast metrics.

A huge key to having success at the game of fantasy baseball is being able to spot outliers. The game of baseball, more than most other sports, is largely dictated by randomness, at least over the short term. Even with the pretty large three-month data sample we have, randomness can still rule the day.

My aim here is to spot some outliers on both sides of the spectrum. The league leaders are approaching 350 plate appearances, which is already surpassing the highest totals we saw in 2020. However, there is still a lot of quirky numbers in the data - so let's check them out.

Before we get to the main event, I'll go through my process here.

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Methodology

I explored what goes into home run totals a bit in the preseason here. I talked about three statistics that are the best predictors of home runs. Those statistics are:

1. Maximum Exit Velocity
2. Fly Ball Rate
3. Average Velocity on Fly Balls

All three hone in on a subset of data - fly balls. Here's a histogram that shows the launch angles of every home run hit since the 2020 season began:

You can see that the vast majority of home runs come between launch angles of 20 and 45. Statcast classifies every batted ball into one of four categories: ground balls, line drives, fly balls, and pop-ups. When we break down all of the 2021 home runs into these classes, we find that 89% of the home runs hit are fly balls, and the remaining 11% are line drives. This being the case, it makes perfect sense to restrict our data to just the fly balls.

It also turns out that maximum exit velocity is a good indicator of power output, as it has proven to be a great indicator of swing speed. Here's the launch velocity histogram on all home runs hit since 2020 (excluding inside-the-park home runs).

You can see there that in rare situations, it's possible to clear the fence with a ball hit in the lower 90's. However, if you really want a legitimate chance for the ball to leave the yard, you have to get above 95. Max exit velocity shows what a guy is capable of. Our third statistic, average exit velocity on fly balls, is a good measure of consistency. Average launch velocity is much more predictive when you restrict the data to just the batted balls that are hit at angles capable of leaving the yard.

I found these three metrics for every hitter with at least 200 plate appearances this year and put together a model to predict home run rates based on those inputs. Then we compare to what has actually happened, take the differences, and look at the players on the extremes. Now, let's get to the results.

Three Up - Hitters to Buy for Home Runs

Keep in mind I am strictly looking at home runs, I'm not saying anything about the ability of these hitters to hit for batting average or anything else.

#1 Jorge Soler, Kansas City Royals

At this point, Soler might just be a career outlier. If you have been trying to predict Soler's future production based on the past data, to this point you've been really wrong every year. Looking at his PA/HR numbers (the league average for this is around 28), it's a rollercoaster ride:

He was one of the premier sources of the long ball in 2019, piling up 48 long balls in 679 plate appearances. Unsurprisingly, he couldn't keep that up in 2020, but he still posted a strong 22 PA/HR between strikeouts (which there have always been plenty of). This year, however, the number has gone completely out of whack to 45. You would think that this has come with a serious change to these three key indicators, so let's take a look.

Yes, he is hitting slower fly balls on average this year than 2019, but not by a ton, and the fly ball rate and max velocity numbers are actually up. He is striking out more as well (26% in 2019, 32% this year), which certainly makes a difference since he's giving more PA's away. All things considered, it does seem like he should be homering at a very high rate, and yet he is not.

League-wide in 2021, 51% of "barrels" (defined as balls in play hit in a certain, optimal launch angle and velocity combination) have gone for home runs. When we look at Soler, only six of his 19 barrels (32%) have found a fence to go over. He does play his home game in one of the bigger ballparks in the league, but this seems like an unsustainable low home run rate on barrels.

You simply will not get a good batting average out of a guy that is striking out 32% of the time, but the home runs should start coming for Soler if he keeps up what he's been doing.

#2 Andrew Vaughn, Chicago White Sox

There was much hype on Vaughn in the pre-season, as his great prospect pedigree and strong Spring Training performance boosted him onto the White Sox Opening Day roster. Playing time was scarce at the beginning, but he's been an everyday player for the Sox for a while now.

He has a disappointing overall line with a .222/.299/.389 triple-slash and just six homers in his 224 plate appearances. However, the numbers suggest much better times are ahead.

First off, Vaughn has a strong 10.7% barrel rate and a manageable 27% strikeout rate. Even better news is that those numbers are both trending in positive directions, here are his rolling numbers in all three (for this, we take his rates from every day of the season, plot them as points, and then draw a line through the points):

Looking at all hitters with more than 200 plate appearances this year and restricting the data to only hitters with strikeout rates under 30%, Vaughn finds himself in 35th place in what I call "optimal contact rate", which is barrel rate plus the second-best kind of contact, defined as "solid contact" by Statcast. That puts him in the top fifth of the league.

He has a max exit velocity of 115 (85th percentile) and an average fly ball velocity of 94.9 miles per hour (74th percentile). The one he has been struggling in a bit is fly ball rate at just 24% (35th percentile). This metric was also trending upwards for him, until recently when it's taken a dip:

Even with his low fly ball rate, my model predicted Vaughn to have a 22 PA/HR rate (the same as guys like Trey Mancini and Teoscar Hernandez actually have this year), and yet his real-life rate sits at 37%. There is a good chance Vaughn really speeds up his home run pace as we head into the second half.

#3 Bobby Dalbec, Boston Red Sox

I almost hesitate to put him on here just because of how crazy his strikeout rate is (38%). It's hard to be sure of anything positive at all when a guy is giving that many PA's away. He is in the running for worst contact hitter in the league. In fact, only Keston Hiura (54%), Taylor Trammell (58%), Mike Zunino (60%), and Javier Baez (62%) have worse contact rates than Dalbec (63%).

The thing that almost balances this out is that he is one of the best hitters in all three categories we're focused on here. Here's how he stacks up:

Only six hitters are above the 80th percentile in all three metrics. Those other names are Ronald Acuna Jr., Shohei Ohtani, Matt Olson, Kyle Schwarber, and Justin Upton.

Dalbec does have an above-average home run with a homer every 25 plate appearances this year, but based on these more granular numbers, that number should be much better. My model had only nine names ahead of him: Shohei Ohtani, Tyler O'Neill, Fernando Tatis Jr., Adam Duvall, Salvador Perez, Kyle Schwarber, Ronald Acuna Jr., Adolis Garcia, and Matt Olson.

The batting average will continue to be anemic with his lack of line-drives, lack of speed, and ludicrously high strikeout rate, but he's a great bet to hit a whole bunch of home runs in the second half.

Other standouts: Jed Lowrie, David Peralta, Niko Goodrum, Gleyber Torres, Gavin Lux

Three Down - Hitters to Sell for Home Runs

#1 Jose Altuve, Houston Astros

Let's just get right into it, here are the numbers on Altuve:

Altuve doesn't make the top half of the league in any of the most important metrics for predicting home runs, and yet he has racked up 17 bombs in 312 PA for an elite 18.4 PA/HR. Home runs in 2021 have traveled an average distance of 401 feet. Altuve has averaged just 388 feet on his home runs, and he has hit five homers on balls that traveled under 370 feet.

There is no reason to rush out to trade Altuve for any old body, because he will likely still say a strong source of batting average and runs scored, but the home runs are hugely bloated - which makes Altuve a great sell-high option right now.

#2 Jared Walsh, Los Angeles Angels

Walsh's strong 2021 campaign has come by a surprise, as he's proven to be one of the best draft values thus far this year. However, he's been struggling of late.

You can see the strikeouts are headed in the wrong direction and the barrel rate has been buoyed by a really hot start to the year. In the table above, you can see Walsh has legitimate pop with solid exit velocity numbers. However, his launch angle distribution makes this high home run rate really hard to believe.

Remember that we are looking for launch angles between 20 and 40 for home runs. There aren't many batted balls falling into that range for Walsh:

So far this year, Walsh has 25 barrels, 17 of which have gone for homers (68%). That is well above the 51% mark we mentioned earlier; Walsh has been the beneficiary of some good fortune this year and makes for a great player to try to trade away.

#3 Eduardo Escobar, Arizona Diamondbacks

Escobar has been a sneaky fantasy player for a couple of years now, belting out 35 homers while hitting .269/.320/.511 in 2019. The home run rate has stayed high this year as he's put 17 over the fence in 309 PAs. His career strikeout rate of 19.6% helps his case, and he hits more fly-balls than almost anybody with a FB% of 36% this year (96th percentile).

The problem is that he just doesn't swing the bat that hard. His max exit velocity is just 108 miles per hour (32nd percentile), and his average velocity on fly-balls is 91.9 miles per hour (33rd percentile).

Right now his PA/HR is in the top 25 in the league, and that just seems very likely to remain the case given the lack of bat speed here.

Other standouts: Buster Posey, Mitch Haniger, Nolan Arenado, Kris Bryant, Jesse Winker, Javier Baez

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