Which pitchers have improved their 4-seam fastballs most?

Almost every pitcher in baseball throws a 4-seam fastball.

In fact, more than one-third of all pitches thrown this season have been 4-seam fastballs.

In this article, I’m going to determine which pitchers have improved their 4-seamers most from 2019 to 2020.

To do so, I will calculate the difference between each pitcher’s 2019 and 2020 trait-based whiff%+, a metric of my creation.

Trait-based whiff%+ for 4-seamers incorporates five variables.

• Average velocity
• Spin per 1 mph/Bauer units (average spin rate divided by average velocity)
• Vertical movement versus average (diff_z)
• RP Z (vertical release point)
• Abs RP X (absolute horizontal release point)

The purpose of this metric is to evaluate which pitchers have the best 4-seam fastballs in terms of their ability to induce whiffs.

The stat does not consider the actual outcomes (how often hitters whiffed) and the location of the pitch.

It grades fastballs on “stuff” alone.

Based on a linear model for which the five variables above are explanatory and whiff% is the response variable, one can see (based on the slopes) that higher velocity, more spin per 1 mph, less vertical movement (more “rise”), a greater absolute horizontal release point, and a lower vertical release point tend to result in a higher percentage of swings resulting in whiffs when it comes to 4-seam fastballs.

Here were the top ten 4-seam fastballs from last season based on trait-based whiff%+ (min. 500 ff)…

1. Jose Leclerc
2. Gerrit Cole
3. Felipe Vazquez
4. Joe Jimenez
5. Hansel Robles
6. Emilio Pagan
7. Tanner Rainey
8. Daniel Hudson
9. Edwin Diaz
10. Aroldis Chapman

The full leaderboard can be accessed here.

Here are the top ten 4-seam fastballs from this season based on trait-based whiff%+ (min. 50 ff)…

1. Trevor Bauer
2. Enoli Paredes
3. Gerrit Cole
4. Max Scherzer
5. Emilio Pagan
6. Jacob deGrom
7. Brandon Woodruff
8. Cristian Javier
9. Drew Pomeranz
10. Chad Green

The full leaderboard can be accessed here.

The metric is very stable year-to-year, which is why I am able to write this article so early in the season. It’s possible, however, that some pitchers may not have reached their maximum strength at this point (could mean their velocity is down). With that being said, many teams have played more than ten percent of their regular season games.

Here is a graph showing pitchers’ 2020 ff trait-based whiff% versus their 2019 ff trait-based whiff%+ …

As you can see, there is a pretty strong correlation (an R exceeding .8). That’s what we’d like to see.

Here are the pitchers that increased their ff trait-based whiff%+ most from 2019 to 2020…

Trevor Bauer (’19: 119 >>> ’20: 150)

Bauer’s velocity is at the same level from last year (up 0.1 mph to be exact), but he is generating significantly more rise on his heater relative to similar ff (1.8 diff_z to 3.3 diff_z). He also increased his bauer units by a substantial amount (4% above league average to 21%) in increasing the spin rate on his 4-seamer. It will be interesting to see if he can maintain such a high spin rate (2817 rpm, up 402 rpm from 2019 and 204 rpm higher than the pitcher with the second highest average ff spin rate (Mike Minor).

Brandon Woodruff (’19: 104 >>> ’20: 123)

Woodruff’s 4-seam fastball velocity is up almost one mph compared to last season (97.2 mph vs 96.3 mph). Like Bauer, he decreased the amount of vertical movement on his 4-seamer compared to similar 4-seamers in terms of velocity and increased the amount of spin he generates per 1 mph.

Jake McGee (’19: 89 >>> ’20: 107)

McGee’s velocity is up 1.1 mph. He increased his diff_z and bauer units as well.

Robbie Ray (’19: 98 >>> ’20: 116)

As many of you may already be aware, Robbie Ray changed his delivery. His vertical release point, as a result is lower, which should translate into a higher whiff% on his 4-seamer. His ff velocity is up over 1.5 mph, and the amount of spin he generates per 1 mph is 6% above league average (it was league average last season).

Drew Pomeranz (’19: 108 >>> ’20: 121)

Pomeranz’s average 4-seam fastball velocity is up around 2 mph. This is probably because he made 18 starts in 2019, and now he is pitching as a full-time reliever. He is releasing his 4-seamer about 2 inches lower than last year.

Zac Gallen (’19: 109 >>> ’20: 119)

His fastball has improved due to reduced vertical movement (less drop/more rise).

I’d rather not delve too deeply into pitchers whose ff have worsened (let’s stay positive), so I will just briefly note them.

• Matt Boyd (’19: 104 >>> ’20: 85) – lower bauer units and lower diff_z
• Mike Clevinger (’19: 120 >>> ’20: 104) – velocity down 1.2 mph, lower bauer units, and lower diff_z
• Chris Paddack (’19: 106 >>> ’20: 91) – lower bauer units and lower diff_z
• Mike Minor (’19: 107 >>> ’20: 93) – velocity down 2.3 mph and lower diff_z
• Nathan Eovaldi (’19: 106 >>> ’20: 97) – velocity down 0.5 mph, lower diff_z, lower bauer units, and higher vertical release point
• Sonny Gray (’19: 108 >>> ’20: 99) – lower bauer units

Here are the gifs for the rest of the top ten 4-seam fastballs

No. 2 Enoli Paredes

No. 3 Gerrit Cole

No. 4 Emilio Pagan

No. 5 Max Scherzer

No. 6 Jacob deGrom

No. 8 Cristian Javier

No. 10 Chad Green