2021 Red Sox Best Four-Seam Fastball Hitters: Part 1

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The 2021 Boston Red Sox roster is consists of some pretty notable hitters. Xander Bogaerts has played much of the season with his average above .300, J.D. Martinez boasts a very respectable .289 career average, and Rafael Devers is a smidge under .280 for his career at .279. There are many ways to classify a great hitter. Guys like Kyle Schwarber and Devers, despite producing similar overall value at the plate, make their hay in different ways. You can exercise your patience, and wait for the pitcher to make their mistake, or can do damage on bad pitches or be the irritant that fouls off their best pitches. But if you want to make things a little more interesting and see who looks like the best hitter, let’s look into who does the best against fastballs?

Hitting a good four-seam fastball is unlike anything else in baseball. By its namesake alone, it tells you it’s fast. It’s not a breaking ball, that can hang for years in the zone. In order to catch up to a fastball, even if it is misplaced takes the most skill. You have to be on time or you run the risk of swinging through or fouling it off. Sure great hitters just don’t hit fastballs, but judging a hitter from a fan’s point of view, fastball hitting takes precedent.

Pitch Values

So then who has been among the best fastball hitters for the 2021 Red Sox? There are many ways to answer this question, so let’s take a crack at it. The first thing we will do is look at the pitch values. Using Pitch Info fastball classifications, here are the Red Sox’s best hitters against four-seamers this year. The data collected is up to August 29th.

Highest FF Pitch Values/100

Player wFA/C
Hunter Renfroe 1.33
Xander Bogaerts 1.29
Enrique Hernandez 1.03
Alex Verdugo 0.95
Rafael Devers 0.84
J.D. Martinez 0.32
Christian Vazquez -.018
*Pitch values allow you to see how “successful” each pitch has been over the course of a season. *Pitch Values are an accounting method for attaching run values to each specific pitch rather than each specific plate appearance.

Okay, it’s not that simple. Pitch values aren’t the end all be all on who is the best hitter for the Sox. The problem with using pitch value is that it is heavily reliant on batted ball results, which takes quite a long time to stabilize. Turning a few seeing-eye singles into outs would have a huge effect on pitch values, though the actual contact quality would be no different. Down the line pitch values would work well but for the sake of this experiment we are not looking for down the line, or for average. Let’s try something else.


To move this forward, let’s incorporate two factors: avoiding strikes and hitting the ball hard on contact. To make sure these two things are weighed equally we will use z-scores. Z-scores show how many standard deviations away from league average each mark is. The thought behind converting these two factors into normalized values lets us combine them. It also takes into account that player skill varies differently in different places.

For strike avoidance we will look at CSW%, the percentage of the fastballs a batter sees that result in either called or swinging strikes. great fastball hitters don’t swing through fastballs without putting a charge into them. Also, a feared hitter doesn’t let a hittable pitch pass by without going all out. Fastball hitters should be doing just that: hitting, not standing at the plate with the bat on their shoulders letting a huge opportunity go by. Who on the Red Sox fulfills this quality best in 2021? Here are their top five hitters with the lowest CSW% on four-seam fastballs, minimum 200 seen:

Lowest CSW% on Four-Seamers

Player CSW%
Jarren Duran 7.6%
J.D. Martinez 8.2%
Xander Bogaerts 8.7%
Enrique Hernandez 8.7%
Kyle Schwarber 8.7%

This group is certainly the more aggressive of the bunch. The most feared hitters aren’t the ones who just offering at the ball the most though. The feared hitters put that exact emotion into opposing pitchers when they swing and make contact. For that, we will dive into another leaderboard.

Smash Rate

We’re going to go into a metric that helps to calculate meaningful contact, contact that’s hard but not do hard it results in a pop-up. This metric captures two variables: balls hit 100 mph or more and between 10 and 20 degrees. Ben Clemens of Fangraphs called this metric smashes.

Smashes are similar to barrels, and the goal of this according to Clemens is to find the most dangerous hitters. Swings are the denominator. The reasoning is that it helps to show a better reflection of who the best hitter is than using balls in play. By this metric, here are the 2021 Red Sox’s best four-seam fastball hitters (minimum 50 swings):

Highest Smash/Swing on Four-Seamers

Player Smashes per Swing
Kyle Schwarber 10.5%
Hunter Renfroe 10.03%
Rafael Devers 8.52%
Marwin Gonzalez 7.92%
Xander Bogaerts 6.55%

With the exception of Gonzalez, no one else on this list would surprise you as one of the team’s top four-seam hitters. Schwarber, Devers, and Bogaerts were All-Stars this year. Not far out of the top five was another one of the team’s all-stars in J.D.Martinez

So that will do it for part one. We covered pitch values, who’s among the team’s best in CSW%, and we put the smashes per swing metric to the test. In part two it will be all about combining the stats and seeing which Red Sox have the z-scores that prove they are the team’s best against the four-seamer.


Main Photo:

Embed from Getty Images

Players Mentioned:

Xander BogaertsJ.D. Martinez, Rafael Devers, Kyle Schwarber, Hunter Renfroe, Enrique Hernandez, Alex Verdugo, Christian Vazquez, Jarren Duran, Marwin Gonzalez