Generally, the productivity of professional baseball players decreases as they move up the minor league system and eventually into the major leagues. However, there is one guy that has been defying this logic for 41 major league appearances now: Brian Duensing. Upon his promotion to Triple-A in 2007, Duensing posted a 3.24 ERA with good control in 116 2/3 innings. In 2008 and the beginning of 2009, he found himself in Rochester once again, but repeating the level wasn’t as kind to him, as he put up a 4.28 and 4.66 ERA, respectively, over an additional 214 innings. His walk rate didn’t change, but he had a drop in strikeouts from about 6.5 per 9 innings to 5 per 9 IP. Despite his perceived struggles (I’ll explained why it was “perceived” later), a rash of injuries to the Twins pitching staff in 2009 led to Duensing making his professional debut.
As a reliever, Duensing wasn’t very effective, but he saw great success as a starter in ’09. A 2.73 ERA starting games for the Twins quickly painted Duensing in a positive light to many fans, and when the 2010 spring training came around, he was one of the candidates to be the 5th starter. Francisco Liriano eventually won that job, but the Twins liked Duensing so much that they put him into the bullpen. It has looked like a great idea so far, as Duensing currently has a 1.69 ERA in 16 innings, with a .166 opponent’s batting average and 0.88 walks and hits per inning pitched. If it wasn’t for Liriano’s own hot start to the season, Duensing would look very deserving right now of being shifted into the rotation. Instead, he has become a valuable pitcher against lefties, sometimes as Ron Gardenhire’s first choice. After I blasted Jim Souhan for thinking that Brian Duensing would replace Jose Mijares as the top lefty in the bullpen, he’s done nothing but dominate.
Remember how I said this was a surprise because Duensing wasn’t so good last year in Triple-A? Well, that 4.66 ERA was accompanied by a 3.21 FIP, meaning that he had been very unlucky, and his success in the majors shouldn’t have been so surprising…except the opposite is true. What I mean is that Brian has been lucky every since he was promoted from the minors. I’ll only focus on Duensing’s 2010 season:
- No home runs allowed, 0.0 home run per fly ball percentage: Clearly neither are sustainable. The MLB average for HR/FB is around 10%, and although it is possible for a relief pitcher to go an entire season without allowing a home run, it’s very rare. It’s possible that Duensing will have a HR/FB below 10%, especially since he had a 6.6 HR/FB last year, but it’s most likely not going to stay at 0.
- BABIP of .199: This is the batting average on at-bats that didn’t result in a strikeout. Again, this is not sustainable. Every season, the major league average is around .300, with a range of about .280-.320. Think Duensing can defy the odds? Even with his good 2009 season, his BABIP last year was .295.
- FIP of 3.12 compared to his 1.69 ERA: Studies have shown that a pitcher’s FIP predicts his future ERA better than his current ERA. A 3.12 FIP is definitely good (FIP is measured on the same scale as ERA), but that’s aided by his lack of home runs allowed. Oh, and if you don’t trust FIP, keep this in mind. With a large enough sample size, FIP and ERA will be identical. (Calculation of FIP found here)
There’s some other reasons why Duensing should regress eventually, but I’m not the right person to discuss those reasons. Don’t get me wrong, though, I’m very pleased with how he’s been pitching in the majors, and I would love for it to continue. The stats just give evidence that it won’t last.