Milwaukee Brewers starting right-handed pitcher Jimmy Nelson has been among Major League Baseball’s best this season in one critical category for starting pitchers: strikeouts.

Nelson is currently 9th overall in strikeouts this season in Major League Baseball, trailing only Carlos Martinez, Zack Greinke, Luis Severino, Jacob deGrom, Corey Kluber, Chris Archer, Max Scherzer, and Chris Sale entering his start on Friday versus the Washington Nationals.

It’s reasonable to expect Nelson to climb up the strikeout leaderboard again Friday night, as Nelson’s 181 punch outs leave him one behind Martinez, and 6 behind Greinke. It’s quite the turnaround for a guy that struggled to keep the ball in the park last year, as well as keep runners from reaching base easily.

In 2016, you could see signs that one day Nelson could turn into a strikeout pitcher, but his command was just to much of a question mark. He wasn’t getting ahead of hitters, and even when he did, he would lose them in the count more times than not. He lead all of Major League Baseball in walks last season, (86) and he and Chris Sale tied to hit the most batters in a season with 17.

2016 was the second straight year that Nelson and Sale lead the league in hit batters, after they both hit 13 in 2015 but were this time joined by Chris Heston and Nick Ramirez. The big difference between Nelson and Sale was that Sale didn’t allow the free pass at a high rate. In fact, Nelson’s 86 walks in 2016 would only be topped by Sale if you add together his 2015 and 2016 walk totals, which only makes it one more walk.

The question many are asking is how did Nelson go from a walk machine with a command problem, to becoming the best strikeout starter on the Brewers roster? Nelson is now on-pace to post the first 200+ strikeout season by a Brewers pitcher since Yovani Gallardo in 2012, and it’s time to take a deep dive into what Nelson has changed to become a strikeout artist.

Perhaps the biggest change from 2016 to 2017 Nelson has made with Brewers pitching coach Derek Johnson helping along the way is simply being able to generate more swings and misses from opposing batters, especially left-handed hitters. From 2014-2016, lefties simply ate up Nelson at the plate, as they posted a .821 OPS against the Alabama product, while right-handed batters had a significantly lower OPS against the Alabama product at .701.

While in 2017 lefties still post the higher OPS against Nelson than right-handed batters, the overall OPS from lefties this season is down almost a full 100 points, while the right-handed OPS has dipped into the 600 range. Collectively this year, opposing batters have a .703 OPS batting against Nelson this year, down 53 points from the .756 OPS hitters had in 2014-2016, which included a .793 OPS in 2014, and a .791 OPS in 2016.

The 28-year-old Nelson is also getting opponents to swing at his pitches that are out of the strike zone at a carer mark this season at 32.9%, and when opponents swing at those out of the strike zone pitches, they aren’t doing what they used to. In 2016, when opponents swung at pitches outside of the strike zone from Nelson, they made contact 70.3%. Now it’s down to 62% this season.

Another change Nelson has made for the better is his ability to hold runners when they do reach base on him. Last year, Nelson allowed 30 stolen bases, but has cut that mark in half to 15 with 5 or more starts still to go. His 43 walks on the year have also been cut down halfway from the 86 mention above in 2016.

Let’s take a look at Nelson’s pitch repertoire now, which features a sinker, fastball, slider, and knuckle-curve as his four main pitches with a change-up making an occasional appearance.

Now, let’s take a look at Nelson’s 2017 chart, and compare the similarities and differences:

The first thing about Nelson’s pitches that should be pointed out is the obvious; there is no drastic change in his velocity. He is still throwing the same speed, and opponents are still having success against the pitch he throws the most in the sinker.

Here’s where the difference maker comes in for Nelson though, as he now has three main strikeout pitches this season, when he only had one in 2016. As we can see in 2016, Nelson’s slider was virtually tough to get the bat on. Opposing hitters only hit .167 against his slider, while Nelson was able to generate 81 whiffs on it, topping the sinker and fastball.

This year, it’s still a lot of the same, as opponents are hitting higher on the slider, but not great at .241. This has become Nelson’s fourth most-used pitch though, as his knuckle-curve has emerged as another strikeout pitch for hitters to deal with. In 2016, Nelson’s knuckle-curve simply wasn’t generating whiffs, and opponents hit .267 against it. But now, Nelson’s knuckle-curve has become Corey Knebel-esque. Knebel, the Brewers closer, leads all Major League relievers in strikeouts with 106, as his knuckle-curve has been a reason why. Opponents are batting just .120 against it, and have yet to hit a homer off it all season.

Back to Nelson, opponents are hitting only .176 against his knuckle-curve, a pitch that has generated the 3rd most whiffs out of any Nelson pitch at 61. The slider comes in at number two with 76 whiffs, but the fastball has taken a big leap to 96 whiffs after only getting 66 whiffs in 2016. There is also just simply more movement on Nelson’s fastball this season.

After pitching 8 innings of one run ball against the Rays on August 6th, Nelson’s earned run average was at his lowest mark since April at 3.24. That ERA took a 50-point spike in the wrong direction in his next start against the Reds, when Cincinnati tagged him for 9 earned runs in just 3.2 innings of work. If you took out that start, Nelson’s season ERA would be 3.32 instead of 3.75.

Regardless of what his season ERA is, one thing can be determined for sure, Nelson has surely broken out this season, and has been Milwaukee’s best pitcher this season with Chase Anderson being a close-second only due to missed time with an oblique injury. Nelson had the Brewers’ first complete game since Taylor Jungmann in 2015 earlier this season against the San Diego Padres, and we can surely expect to see a few more from Nelson down the road.

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*All statistics in this article are courtesy of FanGraphs, Baseball-Reference, and ESPN, and are accurate as of September 1, 2017*