In his first tour of duty in the Major Leagues, Jimmy Nelson has drawn some notice for his somewhat unusual pitch selection. When he was called up (as many of us, including myself, hoped he would be) the conventional thought was that his fastball and slider were plus major league pitches, but there was concern about his ability to find another weapon to be able to use against lefhanders.
I began thinking about other starting pitchers who rely so heavily on their fastball and only one other pitch. It turns out that this is not something that is very easy to investigate because there is a large gray area. I tend to be skeptical of decomposing fastballs into 4-seam, 2-seam, and sinker from an analytical perspective because at the major league level I think there's more of a fastball spectrum than distinct pitches (cut fastballs are generally the exception to my informal rule). So as of yet I have yet to devise a way to look at this at a league-wide level, but I I am going to keep working on that.
While thinking about this, however, a pretty interesting compare/contrast candidate emerged. I thought to myself, "Self, can you think of any former Brewers pitchers who notoriously relied on a fastball/breaking ball combination and could never really develop a third pitch to use as a weapon against lefties? And preferably also was a big righthander from the South who is bad at hitting?"
But maybe the most interesting thing about the Jimmy Nelson/Ben Sheets comparison is actually about the differences in their styles.
Sheets's famous 12-6 curveball was effective against both righties and lefties. In his career, he allowed a .310 wOBA (.251/.298/.420) to lefthanders and a .305 wOBA (.251/.296/.410) to righthanders. That's despite managers stacking lineups with lefties against him; in his career he faced 2887 lefties and 3100 righties. That success against lefthanders is interesting in part because scouts are always telling us that a pitcher absolutely needs a change or splitter to keep opposite-side hitters honest to succeed as a starter. In the limited overlap between the pitch f/x era and the Sheets Brewer era, he threw his changeup to lefties about 3% of the time in 2007 and 8% during his fantastic 2008. In his time with the Brewers overall, the most he ever threw it overall was in 2006 at 6% of all pitches to batters on each side of the plate, according to Fangraphs classifications.
In contrast, Nelson has a fantastic slider that breaks in a completely different way than the trademark Sheets up and down curveball. Perhaps as a consequence, he has shown a persistent platoon split. In the minors in 2013, he gave up a .586 OPS to righties and .715 to lefties. This year in the minors it was .529 against righties and .635 againts lefties. In just over 50 major league innings, he's allowed a .299 wOBA to righties (.260/.330/.323), which is slightly better than the career number for Sheets. Against lefties it's .352 (.268/.339/.459), which is most definitely not better than the career average for Sheets.
While Sheets could have used a more effective changeup as an additional weapon, Nelson may need an effective changeup to take the next step in his development in the major leagues. That's not to say he cannot still be a success story without one. No one says that everybody has to be a Ben Sheets type, who is equally effective against batters from each side of the plate-- very few pitchers are.
There's also another fundamental difference in the styles of these two pitchers. Sheets, as we all remember, was a flyball pitcher. When he got in trouble it was often due to extra base hits, and he very rarely walked anyone. His career OBP allowed was under .300, and slugging well above .400. Nelson has shown the opposite. His ground ball to fly ball ratio is around 1.5 to Sheets's 1.1. His OBP allowed so far in the majors is over .330, but he's held righties to a .323 slugging average. The extra baserunners have gotten him in trouble against lefties, however, who have gotten him for a .339 OBP and .459 SLG.
Even during Nelson's solid but unspectacular run so far in the Major League rotation, he's shown signs of being dominant against righthanders while relying entirely on fastballs and sliders. He has yet to even attempt to throw a changeup to a righty batter in the major leagues, and has thrown a sub-Sheets level of changeups against lefties (as far as I can tell, the total number is 14 so far in his major league career). I have confidence that he can be a solid major league starting pitcher as-is, but if he gets the hang of his changeup at some point and starts throwing it with confidence, watch out.