Quantifying Tyler Thornburg's Improved Fastball

I've always been a fan of Tyler Thornburg. The Brewers' minor league system was pretty lean on pitching prospects in the early part of this decade, but the club's third round pick in 2010 was one worth getting a little excited about. The righty posted a 2.57 ERA in 2011 and a 3.20 ERA in 2012 with gaudy strikeout numbers while rocketing up the ladder in the minors. He made his big league debut at the end of that season and was rated as the club's top prospect according to MLB Pipeline.

Thornburg got an extended trial in the rotation during that 2013 season and was quite impressive, posting a 2.03 ERA and 3.11 FIP in 66.2 innings. He was slated to be the club's fifth starter heading into 2014 until the signing of Matt Garza late in the offseason bumped him out of his spot. Thornburg had worked almost exclusively as a starter up to that point in his career, but rather than keep him in that role the club elected to bounce him into the bullpen.

While he experience a spike in his fastball velocity to a career-high 93.5 MPH, making 27 appearances within the first two months of the season took their toll. He started having elbow troubles and didn't pitch again after June 6th. Luckily Thornburg was able to rehab his partially torn UCL with a PRP injection rather than undergo the dreaded Tommy John surgery. Tyler was ready in time for the start the 2015 season and again started in the Brewers' bullpen.

After a tough first month of the season, however, Thorburg was optioned back to the minor leagues and was yo-yo'd back into the starting rotation in Colorado Springs. He struggled mightily while trying to adjust in his return to the rotation and made 17 ineffective starts for the Sky Sox, posting a 5.28 ERA and 5.91 FIP. After the Brewers' rash of trades before the deadline, he was recalled to the Brewers and again shifted from the rotation to the bullpen. He posted solid run-prevention numbers with a 2.92 ERA in 24.2 innings through the end of the season, but that was not supported by a 4.47 FIP and he averaged just 92.0 MPH on his fastball during that time.

Coming into this season Thornburg is at a make-or-break point in his career. With no minor league options remaining he was all but guaranteed a spot on the team to start the season but if his performance wasn't up to par, he could be faced with the proposition of being exposed to waivers for the first time in his career. Manager Craig Counsell told Thornburg prior to the season that he should focus solely on preparing for a role in the bullpen, ending the back-and-forth from starting to relieving that has plagued Tyler for the last three seasons.

Injuries to Will Smith and Corey Knebel have created opportunity for Thornburg in the late innings of the bullpen mix, and so far he's taken advantage. Now two seasons removed from his elbow injury and after having an entire offseason to prepare for a full-time relief role, Thornburg has come out throwing gas in 2016. His average fastball velocity has jumped all the way up to 94.2 MPH in this season's short sample, a good half-mile faster than his previous career high in 2014. He's hit 96 MPH several times already.

He's only faced 11 hitters thus far, but so far Thornburg's fastball usage has been a little different than previous years as well. Last season, Tyler focused his four-seamer most heavily to the upper and arm-side part of the zone, inside to a right-handed batter. Hitters posted a .280 batting average against it with a .507 slugging percentage according to Brooks Baseball.

So far this season, Tyler has continued throwing heavily to his arm-side with his four-seamer but has lowered the target. He's also added nearly two inches of horizontal break (-0.67 inches to -2.47 inches) to the fastball, giving it a bit of break inside to righties rather than the straight, rising fastball that he featured last year.

Home runs have plagued Thornburg in the past, especially last year, so perhaps the re-location of his fastball is a function of trying to get that issue under control. Still just 27, it also stands to reason that his control may have sharpened a bit as well so he's able to locate his fastball better rather than leave it hanging over the upper-middle part of the zone. Either way the results have been palpable; in addition to his significantly improved velocity, Tyler's whiff rate per swing has increased from 15.06% last season to 23.53% this season on the fastball.

So far during the regular season Thornburg has pitched three scoreless innings with five strikeouts, allowing just one hit and one walk. His improved fastball has even helped his already-plus changeup, which he's used to induce an incredible 63.64% whiffs-per swing in 2016. If Tyler can keep up these improvements as the season goes on, he'll continue to earn high-leverage appearances and solidify his role in the late-inning bullpen mix going forward even as others return from injury.

Statistics courtesy of Fangraphs and Brooks Baseball