Dan Szymborski recently posted the 2020 ZiPS projections for the Seattle Mariners. The system forecasts lefty Marco Gonzales to be the best pitcher on Seattle’s staff. That should come as no surprise considering that Gonzales has been far and away the best arm the Mariners have had to offer lately. According to ZiPS, he’s expected to throw at least 170 innings in 2020 and post a 4.26 ERA (4.12 FIP) with a WAR of 2.6. Despite his strong showings in 2018 and 2019, ZiPS indicates a fair amount of regression for Gonzales this coming season.

After two straight seasons of 3-plus WAR, can we expect a pitcher who throws two fastballs that barely reach 90 mph to maintain that level of performance? Despite his ability to spread his arsenal out, especially when he’s ahead of the hitter, there is a change to Gonzales’ pitch selection that could facilitate another impressive season for the 27-year-old former 19th-overall draft pick.

Gonzales threw five different pitches in 2019: a sinker, cutter, a fading changeup, a sweeping, slurve-ish curveball, and a four-seamer, all with above-average command:

As you can see, Gonzales throws three different fastball variations. His traditional cutter works just fine and by FIP, it was his best pitch in 2019. Its 11:40 spin direction facilitates little sweep but a decent amount of rise.

Gonzales favored his sinker over the four-seamer last year, though he warmed up to the latter as the season wore on. He has a good command of both pitches, though he tended to miss the zone a bit more with the four-seamer. Including his fading changeup, those two fastballs give Gonzales three out of five arm-side moving pitches versus his traditional cutter and sweeping glove-side curveball. The apparent superfluidity of his sinker and four-seamer (along with the changeup) should make him consider limiting one of those options or removing it altogether.

Here’s a look at how the sinker (Pitch 1) and four-seamer (Pitch 2) move in relation to each other using the Driveline Baseball EDGE tool. Both the fastball and sinker average about 98% spin efficiency with roughly a half-hour spin direction difference:

There’s a fair amount of differentiation between the two, but considering that the average spin direction between a sinker and four-seam fastball is about 52 minutes, it reinforces the idea that one should be shelved, save for a special occasion.

Now that we see the general behavior of the two, let’s take a closer look at how each performed last year:

Marco Gonzales 2019 Sinker vs. Four-Seamer Pitch Usage BB/K ISO HR/FB% (FB%) O-Swing% Z-Contact% SwStr% wOBA Sinker 21.3% 0.68 .199 17.5% (32%) 25.8% 89.8% 5.3% .352 Four-seamer 18.3% 0.50 .102 2.6% (48.8%) 20.7% 84.2% 6.9% .283

Despite the sinker receiving more out-of-the-zone swings, it’s clear the four-seamer was the better pitch. The sinker’s biggest drawback was an increase in fly balls, which facilitated his 17.5% HR/FB rate. The rate at which Gonzales threw his sinker in the zone jumped from 47.3% in 2018 to 60.2% in 2019, and hitters made more contact with the pitch (almost 90%). Using Bauer Units to ratio the spin rate to the velocity of Gonzales’ sinker, the pitch produces a score of 25.3. That means he should be keeping the pitch higher in the strike zone than he did last year because of how Magnus Force acts on the pitch. The high spin rate on lower velocity keeps the sinker elevated more than others and essentially prioritizes lift over run.

However, keeping a sinker elevated can cause problems, especially if the spin direction (and gyro degree) aren’t kept constant (Gonzales showed a fair amount of spin direction variation game by game in 2019.). A high sinker that drops too much or doesn’t run enough can fall right into the barrel of a hitters bat.

As for the four-seamer, the pitch did pretty well in 2019. Gonzales held hitters to an 87 wRC+, drew a lot of fly balls while keeping his HR/FB rate to a minimum, and saw overall contact on the pitch drop from 2018. He also kept the pitch elevated a bit more than his sinker, which is a good thing considering their BU scores are essentially the same.

So now that it’s starting to become clear that his four-seamer is the better option, let’s see if the pitch pairs better with the rest of Gonzales’ arsenal.

We’ll first look at his best pitch, the changeup. While the fastball is the foundation on which all other pitches are typically built, we are instead going to focus on which fastball “fits” his best and most-preferred pitch.

Back in 2018, David Laurila interviewed Gonzales, who had this to say about his changeup:

How often I want to throw it depends on the situation, and on the hitter. But I’d like to throw it as much as I can. It’s definitely one of my better pitches. With the help of my curveball, and fastball location… I feel that I have a lot of weapons. So while I’d like to throw it a bunch, I’m not going to rely on it.

Gonzales used his circle changeup more than any of his pitches last year. This well-designed pitch is thrown with a 9:50 spin direction and about 95% spin efficiency. That means Gonzales gets a lot of backspin and side spin on the pitch, facilitating plenty of fade, which hitters often have a hard time squaring up. Gonzales drew whiffs on 22% of swings, though it’s not exactly a strikeout pitch (.301 K/SwStr).

Going back to the design of both the sinker and four-seamer, we see that the differentiation between the sinker and changeup’s spin direction is about 40 minutes, while the four-seamer is an hour and 10 minutes. In most cases, it’s best to have at least an hour spin direction separation with the type of changeup that Gonzales uses. Since both the changeup and sinker fade pretty closely, there doesn’t seem to be enough movement spread between them to create an effective attack. The four-seamer separates from the changeup much more than the sinker does, creating a larger variance in movement:

Then we have the sweeping curveball, to which the four-seamer again matches better. Gonzales throws his curve with a 5:10 spin direction and has significant spin mirroring potential despite a heavy gyro component. (It should be noted that the sinker doesn’t pair badly with it, per se, it’s just that the four-seamer’s design pairs much better.)

After the suggested adjustments, here’s a look at Gonzales’ refined arsenal. Two arm-side pitches (four-seamer and changeup), a pitch with a tad bit of glove-side sweep (cutter), and the slurve/curveball glove-side low; a good spread of effective movement patterns:

Gonzales put together a couple of good seasons in 2018 and ’19. His sequencing and pitch selection played a big part in that, especially considering his fastballs aren’t up to snuff velocity-wise. With three options for his fastballs, it might be a bit overkill to use them all, especially since one pairs the best with the rest of his arsenal. ZiPS expects Gonzales to take a step back in 2020, but how much regression he actually experiences (if any at all) might depend on his ability to focus his fastball attack with his four-seamer with some cutters and sparing use of the sinker.