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Profiling the Cardinals’ new bullpen arm Zach Duke

Given yesterday's acquisition, let's get acquainted with the repertoire of Zach Duke...

MLB: Chicago White Sox at Oakland Athletics Kelley L Cox-USA TODAY Sports

Yesterday, the Cardinals acquired left-handed reliever Zach Duke from the White Sox in exchange for speedy Triple-A outfielder Charlie Tilson. The red baron already provided his initial thoughts on the trade yesterday, and despite being a pretty big fan of Tilson, I cannot help but agree with the points laid out in RB’s article. Plus, the following tweet by David Cameron of FanGraphs does a solid job at explaining the "deal" John Mozeliak and the Cardinals received in what appears to be a "sellers market."

That being said, we do not need another think piece on the Duke acquisition. The trade happened, in similar fashion to many near-deadline deals made by the Cardinals over the years (Edward Mujica, Steve Cishek, Jonathan Broxton, etc.), and on paper, it makes sense. Why does it make sense, some Tilson fans may be asking? Well, Duke, who never quite made it as a starting pitcher, has proven to be an effective reliever against batters on both sides of the plate -- a welcome addition to any club, especially one looking to make a playoff push. Using PitchF/x data readily available on, let’s take a closer look at the Cardinals’ new bullpen arm.

2016 PitchF/x Basics

Remember: Regarding horizontal movement in left-handed pitchers, a positive value means arm-side movement, whereas a negative value means glove-side movement.

Pitch Type Frequency Velocity (MPH) Dragless Horizontal Mov. (in.) Whiffs/Swing
Fourseamer 9.95% 89.95 5.72 43.48%
Sinker 47.24% 89.98 12.83 15.67%
Changeup 3.48% 85.63 11.85 11.11%
Slider 16.75% 81.69 -6.78 34.55%
Curveball 22.59% 75.90 -12.49 43.86%

Most side-arming lefty relievers utilize two pitches: fastball and slider (à la Randy Choate). The fastball is primarily used to keep hitters honest by getting in-the-zone strikes, while the slider is a sweeping one (from left to right), thrown in hopes of getting a left-handed batter to expand his zone off the plate -- leading to zero, or at the very least, weak contact. As a former starter, this is not the case for Duke.

In fact, Duke is able to throw five different pitches (with none of them being straight), with each one being effective in their own way. What is most impressive is the fact that the repertoires of left-handed relievers are usually hamstrung by batter handedness, meaning that while the pitcher in question can go to his slider over and over against lefties, he is not comfortable using it with righties at the plate (mainly due to ineffectiveness). Again, with Duke's history as a starter, this does not appear to be an issue. Now, he does throw certain pitches more frequently with righties at the plate (namely the fourseamer and changeup), but none of his five pitches are completely neutralized, signifying a more complex repertoire than what is usually seen from a left-handed reliever.

With the complexity of Duke's repertoire in mind, it is not surprising to see that he has been effective against both lefties and righties in 2016:

Vs. LHB 77 .260 .299 .347 .281
Vs. RHB 82 .177 .325 .333 .284

We are obviously dealing with small sample sizes here (meaning no real conclusions can be drawn just yet), but Duke appears to be the type of acquisition in which his availability will make bullpen decisions as easy as possible for manager Mike Matheny. Given Matheny's thoughts on LOOGY Randy Choate prior to last season, it's probably best to employ a reliever who is comfortable against batters on both sides of the plate.

Killing worms

Duke Launch Angle

There is a beta feature on that helps provide a basic description of a given pitcher's repertoire -- going through each pitch individually. The description is helpful to those who don't want to dig into (or don't necessarily understand) the PitchF/x data associated with each pitch. Two words popped up for each one of Duke's pitches: "worm killer."

In weird baseball terminology, a pitch that is considered a "worm killer" is one that frequently results in ground balls. Thus, when Duke isn't inducing swings and misses (a method he frequents considering his 26.4% strikeout rate), the balls in play against him are often on the ground. This is evident by the launch angle chart embedded above (retrieved from Daren Willman's Remember, anything below 10 degrees is considered a ground ball.

As is customary for one of my PitchF/x articles, let's conclude with some GIFs for your viewing pleasure, courtesy of, you guessed it,

92.7 MPH sinker to Dustin Pedroia

Despite poor location (essentially middle-middle), Duke was able to strike Pedroia out by blowing a 92.7 MPH sinker past him, largely because he set the put-away pitch up with breaking balls on the pitches prior.

81.2 MPH slider to Ryan LaMarre

In a 1-2 count, with two outs and the bases loaded, it is okay to "waste" a pitch. Based on its final location, that's basically what Duke did here, but fortunately for the White Sox, this "waste" pitch looked good enough (in fact, it was much closer to the strike zone than the previous two pitches) to the batter through its entire flight to home -- starting on the outside corner, sweeping from left to right, only to fall off the corner, down and in.

90.7 MPH sinker to Mike Moustakas

After rocking Moustakas to sleep with ~77 MPH curveballs on the two pitches immediately prior, Duke again was able to blow his sinker by a quality hitter for strike three. It certainly helps that he nailed the catcher's target just off the outside corner (in a virtually unhittable location), but from purely a sequencing standpoint, this was a textbook approach by the 33-year-old lefty.

77.3 MPH Curveball to Alex Gordon

Duke didn't quite hit the horizontal component of the catcher's target here, but after a curveball in the dirt on the pitch prior, this pitch clearly got the job done.

Bottom Line

The trade isn't nearly as flashy as the Indians' acquisition of Andrew Miller, but there is still plenty to be excited about here. With Seung Hwan Oh, Kevin Siegrist, and now Zach Duke, Matheny now has three quality relievers available for use in high leverage situations. Let's hope that is enough to keep the manager from deciding on Broxton for these types of situations.

Credit to for the PitchF/x data and for the GIFs.