Matt Shoemaker did a little bursting onto the scene act last year. He made one start in 2013 but opened 2014 in the bullpen. He made only three appearances before being shipped off to AAA to get stretched out as a starter. Shoemaker returned in mid-May of 2014, after which he remained on the big league team. Yet, he shuffled between some relief appearances and starts, but he mostly started.
As a starter, Shoemaker was pretty solid. In his 20 starts, Shoemaker went for 121.1 innings with a 22.8 percent strikeout rate and 4.4 percent walk rate. His ERA/FIP/xFIP was 2.89/2.88/3.24, and he finished with 2.7 fWAR as a starter. Shoemaker did a good job of limiting home runs. He showed a slight tendency for fly balls with a 41.9 percent ground ball rate, but that's not a strong fly ball tendency like Jered Weaver, who had a 32.9 percent ground ball rate the same year. 2015, for some reason, is different.
As of Monday, Shoemaker has the lowest ground ball rate among qualified starters at 28.2 percent. To give you some context, I grabbed all pitchers who count as "qualified" in both 2014 and 2015 so far (linked dataset does not eliminate pitchers who qualified for only one season; that work was manual in Excel). That is a group of 67 pitchers, which did not include Shoemaker himself. Out of those 67 pitchers, only Jeff Samardzija has had a larger decrease in ground ball rate; his decrease was by 13.8 percentage points, while Shoemaker's decrease has been 13.7 percentage points. In other words, Shoemaker almost ties the leader in terms of decreased ground ball rate. It's been a sharp decrease in ground balls.
My first inclination is to visit Brooks Baseball to check for any major changes in the regular indicators like usage rates or movement or location. Shoemaker has actually increased his four-seam usage from last year, and his four seamer is generating fewer ground balls per ball in play than last year (27.2% --> 6.1%). For what it's worth, Shoemaker's sinker is also generating fewer ground balls per ball in play (45.5% --> 21.1%). Movement is fairly stable.
The next thing I look at is location. Shoemaker has always kept his four seamer up in the zone; it's possible he has tried to locate the pitch differently, especially against lefties. The following two images show Shoemaker's four-seam locations in 2014 and 2015 against lefties.
Focus on the high and away part. It looks like Shoemaker has increased his concentration on those 3 squares and can hit that spot with regularity. That would certainly lead to some more fly balls.
Of course, this early in the season, the small sample size caveat still applies. While there is some evidence of what you might call true "cause and effect", like increased four-seam usage, there is a sample size artifact present. Specifically, Shoemaker has faced teams who like to hit fly balls.
In his seven starts, Shoemaker has faced Seattle twice, Oakland twice, and Texas, Houston, and Baltimore once each. The Astros, Rangers, and Mariners show up in the top 5 teams by fly ball percentage; the Athletics and Orioles rank 12th and 13th, respectively. Flipping the ranking to ground ball rate, since the distinction between line drives and fly balls can sometimes be blurred, those teams still lean toward balls in the air. Texas (15th), Oakland (19th), Seattle (20th), Baltimore (21st), and Houston (29th) are not teams that hit a lot of ground balls.
So, you have a pitcher who already leaned a bit fly ball, appears to have made conscious changes to generate more fly balls, and has faced fly ball-leaning teams. That's how a big change in ground ball rate is made.
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Kevin Ruprecht is the Managing Editor of Beyond the Box Score. He also writes at Royals Review. You can follow him on Twitter at @KevinRuprecht.