Thanks to brooksbaseball.net (Gibson, Morton, and Perez) and Fangraphs for the data.

You know the profile of a sinkerballer, the low-90s fastball, no strike out pitch, and wildly inconsistent. It fits the mold of the newest Twin, Martin Perez, whose career struggles have led many to question the move. Here, I offer a rationale for the move using two previous sinkerballers who changed their repertoire and transformed their careers through increased velocity and relying on a breaking pitch to strike hitters out.

It's important first to distinguish Perez's career pitch percentages in comparison to Morton's and Gibson's at the points of their transitions in repertoire.

• Kyle Gibson (career through 2017):
  

1. Sinker-41.4%
   
2. 4-Seam-17.82%
   
3. Changeup-16.04%
   
4. Slider-20.06%
   
5. Curve-4.68%
   
6. Avg. Sinker Velocity: 92.2 MPH
   
7. ERA: 4.70
   
8. K%: 16.0%
   
9. K/9: 6.2
   
10. FIP: 4.35
    

• Charlie Morton (career through 2016):
  

1. Sinker: 48.6%
   
2. 4-Seam: 17.26%
   
3. Changeup: 4.03%
   
4. Slider: 1.35%
   
5. Curve: 20.07%
   
6. Cutter: 3.29%
   
7. Split: 5.31%
   
8. Avg. Sinker Velocity: 92.14 MPH
   
9. ERA: 4.54
   
10. K%: 16.0%
    
11. K/9: 6.3
    
12. FIP: 4.10
    

• Martin Perez (career):
  

1. Sinker: 37.52%
   
2. 4-Seam: 23.33%
   
3. Changeup: 19.37%
   
4. Slider: 10.89%
   
5. Curve: 8.89%
   
6. Avg. Sinker Velocity: 93.16 MPH
   
7. ERA: 4.63
   
8. K%: 13.9%
   
9. K/9: 5.46
   
10. FIP: 4.44
    

My jaw just about dropped when looking at the numbers. All three used the sinker around 40% of the time. Perez used his 4-seam a little bit more and had a bit more velocity. Outside of velocity, Perez's percentages are much worse. His K% and k/9 are below both Morton and Gibson. His ERA is directly in between the two and his FIP is the worst amongst the three, chalk it up to relying on weak contact being made and defense being on his side. Also interesting to me was that Gibson's slider and Morton's curve, effectively their swing and miss pitches, were used at basically the same percentage! Morton and Gibson also had almost the exact same k/9 and sinker velocity and their K% WAS THE EXACT SAME at 16%! As you can see from the ERA and FIP, their repertoire made them average at best and more commonly mediocre because they relied on defense to bail them out. For both of them, change was needed and as results have shown, were effective.

Charlie Morton signed with the Houston Astros in 2017. The changes Houston made were immediate and effective. Over the 2017 and 2018 seasons, here were the results.

1. Sinker: 35.15%
   
2. 4-Seam: 21.04%
   
3. Changeup: 0.19%
   
4. Slider: 0.52%
   
5. Curve: 29.15%
   
6. Cutter: 8.07%
   
7. Split: 5.85%
   
8. Avg. Sinker Velocity: 95.42 MPH
   
9. ERA: 3.36
   
10. K%: 27.7%
    
11. K/9: 10.4
    
12. FIP: 3.53
    

Houston helped Morton design a delivery that increased velocity, while decreased sinker usage and increased 4-seam usage helped increase velocity as well. Notice that Morton did not sacrifice the sinker, it's still his most used pitch. However, it's been made more effective by increasing the usage of his curve. Morton's curve in 2017 and 2018 had a whiff percentage of 18.67%. Houston realized that increased curve usage would help Morton get more swings and misses. It has led to Morton striking out an additional 10% of the batters he faces and also 4 more strikeouts per 9 innings while increased usage of the cutter and split have resulted because those two pitches generate whiffs as well. Morton went from a mediocre major leaguer to a rotation regular and potential all star by changing his repertoire and increasing the use of pitches that generate swings and misses.

While Kyle Gibson didn't see the large velocity increase that Houston's program did in helping transform Morton, a noticeable uptick in velocity as well as better slider usage led to a career year. Here's Kyle Gibson's 2018 numbers in the following categories:

1. Sinker-33.93%
   
2. 4-Seam-23.84%
   
3. Changeup-11.01%
   
4. Slider-21.01%
   
5. Curve-10.21%
   
6. Avg. Sinker Velocity: 93.42 MPH
   
7. ERA: 3.62
   
8. K%: 21.7%
   
9. K/9: 8.19
   
10. FIP: 4.13
    

Gibson's numbers didn't jump to the extent of Morton, but they're nothing to slouch at either. Like Morton, Gibson reduced usage of his sinker and a mechanical change led to a slight uptick in velocity. Where Gibson reduced fastball usage, he utilized his breaking ball. The Twins noticed something in Gibson's slider and for good reason. His slider generated whiffs an INSANE 27.17% of the time in 2018, no doubt one of the best sliders in MLB. However, Gibson didn't use it that much more in 2018 than his career before 2018. I think the Twins have changed how it gets used. It no longer is used as a get me over pitch, it is used to put hitters away and has become extremely effective as a result. Gibson also had a whiff rate of 18.11% with the 4-seamer and a whiff rate of 18.21% with the changeup, establishing two more pitches that can generate swings and misses. One of the things I noticed also was an increased use of the curve in 2018. While it's not as effective at generating swings and misses, it provides another pitch in the repertoire to deceive hitters. My hope in 2019 is that Wes Johnson can work some magic and increase Gibson's velocity in 2019..

What should the Twins do in 2019 to Martin Perez to see results similar to Gibson and Morton? I propose a few things.

1. Change his mechanics to increase velocity.
   
2. Decrease use of the sinker while increasing 4-seam use.
   
3. Determine a swing and miss pitch for Perez that either gets increased use (like Morton) or is designed specifically to put hitters away (like Gibson). His changeup looks to be the most promising, generating a whiff rate of 17.12% in his career.
   

Obviously, his performance is yet to be seen, but I think this is along the lines of the rationale the Twins signing Perez. If he's going to find success, I think this is the way.