Jordan Zimmermann Having Career Year in Loaded Nats Rotation

The Washington Nationals starting pitchers have had a remarkable year. Their 14.5 fWAR leads the National League. Stephen Strasburg is among the league leaders in strikeout rate, Tanner Roark has a sub 3.00 ERA, Doug Fister has accumulated 3.5 RA-9 WAR despite missing a large chunk of the season, and Gio Gonzalez has a strikeout rate just shy of 25 percent. However, the best performance has come from Jordan Zimmermann.

The 28 year-old Zimmermann broke into the major leagues in 2009. But, he suffered an elbow injury that required Tommy John surgery, and he missed the remainder of that season and most of 2010. He returned to full strength in 2011, and from 2011-13, he authored a 3.12 ERA with 10.2 fWAR. Zimmermann relied on a strikeout rate that was in line with the major league average and a 4.9 percent walk rate that was one of the lowest in MLB.

This season Zimmermann has managed to cut his usually low walk rate to a miniscule 3.8 percent. At the same time, he’s boosted his strikeout rate to 22.6 percent, which is a solid four percentage points higher than the previous year. As a consequence, he’s dropped his ERA to 2.93, and his xFIP to a career low 3.07, which is nearly half a run lower than his previous best. His 4.3 fWAR is a career-high, and he ranks 11th in the major leagues in that category.

Zimmermann has made two significant changes. First of all, he is throwing his fastball more often. At 69.5 percent, only five qualified starting pitchers utilize their heater more frequently than Zimmermann. With an average velocity of 94 miles per hour, only ten pitchers have a harder fastball. He’s getting more whiffs with the pitch. It’s missing bats at an 8.3 percent clip as compared to 6.2 percent, and he’s also getting more infield pop flies.

Also, Zimmermann is throwing his slider harder. Zimmermann’s slider has long been his best secondary pitch, and he usually throws it around 86 miles per hour. This year he has bumped that velocity up to 87.5 miles per hour and as a result he’s getting more swings and misses. Batters have a whiff rate of 18.5 percent on Zimmermann’s slider, as compared to 16.3 percent the prior year and 13.9 percent in 2012. In addition, they are chasing the pitch nearly half the time when it’s located out of the strike zone, a big jump from past seasons.

Thanks to the fastball and the slider, Zimmermann’s overall whiff rate has increased from 8.7 percent to 10.2 percent. Interestingly enough, while his first-pitch strike rate and walk rate have improved, his zone rate is down. He’s been able to get ahead of hitters and then use his slider to expand the zone. Jordan Zimmermann has been a very good pitcher for the last three seasons, but the increase in whiffs has helped turn him into an ace.