Bobby Jenks: Finesse Pitcher?

As a member of the Angels organization, right-hander Bobby Jenks was something of a mythological figure. The gargantuan 6-3, 280 pounder, selected in the 5th round of the 2000 amateur draft, often had radar guns begging for mercy as he sat in the upper-90’s and hit triple-digits on occasion. With that hopping heater, Jenks mauled minor league hitters (9.4 K/9), but his control (an astounding 6.01 BB/9) and temperament left much to be desired.

Despite Jenks’ gifts, the Angels eventually grew tired of the flame-thrower’s antics and punted him off the 40-man roster in December of 2004. The White Sox stepped up and claimed the volatile-but-talented arm, and the club has been rewarded handsomely for its leap of faith.

Jenks burst onto the scene during Chicago’s World Series run in 2005, punching out 11.44 batters per nine innings in 39.1 frames. His control (3.43 BB/9) was just fair, but he managed a 2.69 FIP while showing off a 97 MPH fastball as well as two hard breaking balls (an 88 MPH slider and an 83.5 MPH curve).

The portly righty displayed many of the same attributes in 2006. In 69.2 innings, Jenks used a slightly-less searing 95.8 MPH heater and his hard breaking stuff to post rates of 10.33 K/9 and 4.0 BB/9. Despite the occasional bouts of wildness, Jenks used his ability to miss bats and a newfound tendency to keep the ball on the ground (his GB% improved from 44.6% in ’05 to 58.8% in ’06) to compile a 3.20 FIP.

After two seasons of dominating hitters and allowing a few too many free passes, Jenks performed like a different sort of hurler in 2007. His K rate fell precipitously, from over 10 K/9 down to 7.75. However, he cut his walk rate by more than half (1.8 BB/9) and continued to burn worms (53.8 GB%). Jenks’ blistering upper-90’s cheese was now sitting in the 94 MPH range. The shape of his production was different, but Jenks posted the best K/BB ratio (4.31) and FIP (2.56) of his career.

2008 continued Bobby’s trend of missing fewer bats. A few short years after posting a double-digit whiff rate, Jenks struck out just 5.55 batters per nine innings, while walking 2.48 per nine. His groundball rate (57.6%) remained quite high and his FIP was still a fair 3.41, but clearly the present version of Jenks is not the same fire-breathing mountain man that was on display in Los Angeles’ farm system or in Chicago during his early days there. Jenks was once fairly difficult to make contact with, but opposing hitters have progressively had an easier time putting the bat on the ball:

Jenks’ Contact Rate, 2005-2008:
2005: 74.5%
2006: 77.8%
2007: 79.1%
2008: 84.5%

Jenks’ 2008 contact rate was one of the highest among all relievers. Residing close to Bobby were names such as Ryan Franklin, Brian Bass and Franquelis Osoria.

Bobby Jenks’ transformation from flame-throwing folklore to finesse pitching has been fascinating to watch. Chicago’s plus-sized closer has remained effective to this point (his 3.47 WPA in ’08 was a career-best), but it would probably be best to tread cautiously here instead of investing a high pick. Jenks could well remain effective with plus control and groundball tendencies, but his descending strikeout rate and back issues bear watching.

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A recent graduate of Duquesne University, David Golebiewski is a contributing writer for Fangraphs, The Pittsburgh Sports Report and Baseball Analytics. His work for Inside Edge Scouting Services has appeared on and, and he was a fantasy baseball columnist for Rotoworld from 2009-2010. He recently contributed an article on Mike Stanton's slugging to The Hardball Times Annual 2012. Contact David at and check out his work at Journalist For Hire.

3 Responses to “Bobby Jenks: Finesse Pitcher?”

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  1. Rick Berdelle says:

    Its interesting that Bobby’s contact % has gone up while he has had such a drastic drop in LD%. Do you think the drop in LD% from over 25% down to 14% is due to more movement on his fastball? Can anyone break down his PitchFX data to see if as his fastball velocity decreased his movement increased? Seems like he is allowing weak contact. His BABIP went from the mid .300s in 2005 and 2006 to the mid .200s in 2007 and 2008 as well.

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  2. W. Jones says:

    Dude, enough with the “fat” asides (portly, plus-sized, etc.). Have you ever seen Jenks in the locker room? I doubt it. From the neck down, there ain’t much fat left on him. I would bet a week’s salary that his body-fat % is far lower than yours.

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  3. A quick pitch f/x impromptu analysis shows that in 2007, Jenks had a fastball that had a WHIFF (swing and misses) or .142 (or 14.2%). This past season, Jenks saw his fastball WHIFF drop from the .142 to 0.090 (or 9.0%). He does have a sinking fastball which coupled with the additional contact and the groundball tendencies, could have led to the spike in GB%. In addition to the fastball, Jenks toned down his use of the slider over the course of the past two seasons. In 2007, Jenks used his slider 20.6% of the time. That year it had a WHIFF of .338 (or 33.8%). In 2008, Jenks deployed the slider only 13.8% of the time and saw his swing-and-misses drop (.136 or 13.6%). Furthermore, the 2007 version obtained outs 86.8% of the time it was put into play. Last season it was converted to an out only 63.6%. Of course, considering it was a slider, it was probably of the non-damaging groundball variety when put into play resulting in a harmless base hit.

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