Brian Duensing's very good slider

After slipping into the rotation in late July in the place of an ineffective Nick Blackburn, Brian Duensing has provided the Twins with nothing less than consistent performances. Thus far, the 27-year-old has helped the team continue the second-half surge by supplying an 8-3 record in his 11 starts. Although last night’s outing against Cleveland witnessed his control wane throughout his six innings of work -- as evidenced by his four walks -- for the most part the lefty kept the lineup off-balanced to scatter three earned runs on six hits, recording his seventh victory as a starter.

How does a pitcher like Duensing, who doesn’t have overwhelming velocity and pitches to contact, manage to procure such a solid 3.99 xFIP?

Admittedly, there is an element of luck (or rather, things going his way) in his limited capacity this year. First, Duensing had the advantage of being a situational lefty for an extended period helping pad his statistics in favorable match-ups in the first-half of the season. Also, considering that his left-on-base rate of 82.8% is well-above the league norm of 72.1% in addition to a tidy .275 BABIP contrasting with a .302 league average, one can easily conclude that the long-term results will probably not jive with his current output.

Breaking down his batted ball statistics further, we find that the southpaw has had the benefit of some extraordinarily good defense when it comes to grounders. As a groundball-leaning pitcher (51% groundball rate), Duensing has been supported by a miniscule .199 BABIP on those grassburners while the remainder of the league has an average of .234 on those as well. This is a testament to the above average up-the-middle combination of J.J. Hardy and Orlando Hudson who have, for the most part, been healthy in the second-half of the season. Eventually, even with the middle infield guardians with his back, this number will likely equalize resulting in a few more hits and fewer runners stranded on base.  

Of course, there is also little indication that he will regress that hard either.

Part of the reason for what makes him such an effective pitcher is his possession of a very good slider. When the announcement was made that Duensing would move to the rotation, Fangraphs.com analyst (and former Inside Edge writer like myself) David Golebiewski relayed that back in 2007, Baseball America graded out all of his pitches to be “average or a tick above at times.” While there may be nothing devastating about his slider visibly (unlike Francisco Liriano’s which bends both space and time), the numbers clearly indicate that Duensing’s offering is better than advertised (or, at least, better than perceived).

According to Fangraphs.com’s Pitch Value, Duensing’s 12.7 runs above average on his slider is the fifth-best among AL pitchers with a minimum of 100 innings. What’s more is that only Liriano (21.7 runs above average) and New York’s CC Sabathia (15.5) are the only two left-handers with better totals on their sliders.

When he was mainly working to lefties out of the bullpen, Duensing demonstrated that he was extremely tough on his wrong-handed brethren – particularly with that slider. Lefties have been fortunately enough to hit just .102 (224 OPS) off of his slider, missing on 44% of their swings (versus a 31% league average in that category). This continued into his starting role as opposing managers recognized how lethal he can be on the lefties and has since seen a reduction in the amount of those match-ups.

This is fairly comparable results to the damage Liriano has inflicted with his slider:

Duensing & Liriano’s Slider: Side by Side Comparison
	OPS	Chase%	Miss%	Well-Hit Avg
B. Duensing	272	35	40	.148
F. Liriano	436	45	47	.117
League Average	614	31	31	.167

Naturally, there is plenty of difference in the duo’s sliders and their deployment. While Duensing avoids throwing his to righties (13% of pitches), Liriano has no qualms tossing his (29% of pitches). Likewise, Liriano favors his pitch whenever he has two-strikes (51% thrown with two-strikes) on a hitter while Duensing still uses his fastball more frequent over his slider (27% thrown with two-strikes). Physically, while Liriano’s pitch is thrown at a greater velocity (85.9-mph) than that of Duensing’s (81.6-mph), Duensing’s slider has a greater vertical drop and a bit more pronounced horizontal movement on average according to pitch f/x.

So while Liriano’s slider is obviously the crème-de-la-crème of baseball, Duensing’s slider has been outstanding in its own right. As the Twins start planning on the postseason rotation, they have two very formidable left-handed starters capable of silencing left-handed bats – be it Carl Crawford, Carlos Pena, Robinson Cano or Curtis Granderson – providing an advantage in the short series.