Since joining the Chicago Cubs in a midseason trade in 2013, Jake Arrieta has become more of the pitcher that the Orioles hoped he would become.
In 3½ seasons in Baltimore, he went 20-25 with a 5.46 ERA. In about two years with the Cubs, Arrieta is 21-12 with a 2.89 ERA.
What has made Arrieta a better pitcher?
In a sabermetric piece at mlb.com, Mike Petriello points to some factors that have a lot to do with Arrieta’s pitch selection and what those pitches are doing.
The first big change has been less reliance on his fastball. As an Oriole in 2011, Arrieta threw it 35 percent of the time. This year, the fastball makes up just 10 percent of his pitches.
Though Arrieta was known for his fastball as he rose to the Orioles, once in the majors, that pitch was above average, but not outstanding. By measures of velocity and spin rate, Arrieta ranks in the 70 to 75th percentile of major leaguers who regularly throw four-seam fastballs. So he wasn’t having great results.
But when it comes to his other pitches, Arrieta ranks among the majors’ elite in spin and/or velocity. His sinker and changeup are top 10 in both, curve eighth in spin and slider third in velocity.
Petriello points out that a lower spin rate is actually what a pitcher usually wants on sinkers and changeups, making them drop more quickly. However, because Arrieta’s pitches are staying up longer — often an invitation for trouble — he may be benefiting.
“Arrieta's change and sinker come in harder and with higher spin than batters are used to seeing, and they're having trouble compensating, likely because it's a different look,” Petriello writes.
One sign that this is happening: When batters connect with Arrieta’s sinker, they don’t hit it very hard. His exit velocity — measuring the speed of balls off the bat — on the sinker is better than all but one starter in the majors.
The switch apparently has come on for Arrieta. Unfortunately for the Orioles, it didn’t happen until after he left Baltimore.
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