Jimmy Nelson of the Milwaukee Brewers Could Be Headed for a Breakout

Thanks in large part to a new curveball, Jimmy Nelson has been among the best pitchers in baseball at generating swinging strikes, and an uptick in strikeout rate may soon follow.

With his 4.03 ERA on what has been baseball’s worst team so far, you would be excused for not being excited about Brewers starter Jimmy Nelson.

He is striking out 21.2% of the batters he has faced but also walking 10.6%, good for a 92 FIP- and 103 xFIP- to complement his 105 ERA- in 22.1 innings this year.

Nelson frankly does not seem like a big deal...until you start looking at the rate at which he has missed bats this season.

The 25-year-old, who made 12 starts as rookie last year, has generated a whiff on 30.71% of opposing swings, good for seventh-best among the 152 starters who have thrown at least 100 pitches in 2015, according to Baseball Prospectus.

The next two pitchers on the list are Corey Kluber and Felix Hernandez. Getting a bit more interested?

In terms of swinging strikes as a percentage of total strikes thrown, Nelson also ranks seventh, sandwiched between Hernandez and Chris Sale, according to Baseball-Reference.

How about now?

The swinging strikes are significant, as with better sequencing going forward, we should expect Nelson’s overall strikeout rate to improve, taking his FIP and ERA with it.

Swinging strike rate is very reliable and has a high correlation with actual strikeout rate, as Mike Podhorzer writes at FanGraphs. Blake Murphy of Beyond the Boxscore reached a similar conclusion with regards to whiff and strikeout rates.

Also, since these stats are based on individual pitches, they naturally build a large sample quickly, making them more trustworthy early in a season than other, more commonly-cited stats (looking at you, ERA).

Perhaps now you are more excited about Nelson, but you may also be asking yourself where this is coming from. Last season, he struck out 18.2% of the batters he faced, with a whiff rate of 21.31%, ranking 119th among the 259 starters who threw at least 100 pitches, while his swinging strike rate of 15.7% was below the National League average.

What has changed?

In a rare case in which there may be a clear answer to this question, the catalyst certainly seems to be a newly found curveball.

Nelson had not thrown a curve in his previous 79.1 big league innings but has thrown the pitch 23.77% of the time this season, according to Brooks Baseball.

It has been an incredibly effective pitch, generating a whiff per swing rate of 52.17%, third among the 39 pitchers who have thrown at least 50 curveballs this season.

Eno Sarris of FanGraphs also noted the above average velocity and movement of Nelson’s curveball.

The pitch has become a good complement to his slider, another pitch that generates swinging strikes. In his 12 starts last season, Nelson threw the pitch 270 times and got a whiff on 42.75% of opposing swings, 13th-best among starters who threw at least 100 sliders.

This season, he is throwing his slider less frequently (14.81% of the time compared to 25.07% last season) but is producing a 44.83% whiff rate with the pitch.

While his sinker usage is down to 34.88% from 57.35% last season, it is still his most frequently used pitch in 2015 and has been similarly effective in terms of missing bats (with a 23.08% whiff rate that ranks second in the league among the 96 starters who have thrown the pitch at least 50 times this year).

The sinker also has produced a 72.0% ground ball rate, combining with Nelson’s slider (62.50% grounder rate) and curveball (50.0%) to produce a 57.1% overall ground ball rate, which is tied for 13th among qualifying pitchers.

Nelson is not a finished product yet -- his walk rate is 16th worst among qualifying pitchers -- but if he can improve his control (conceivable, given his 6.1% walk rate last season), we could start to see the whiffs yield big strikeout totals.

Get excited.