Kenley Jansen’s Dominant Fastball

Every year it seems we hear about a former position player trying to transition to the mound in order to save his professional career.

Two years ago, it was Tony Pena Jr. with the Royals who moved from a light-hitting shortstop to reliever. In 2010, Sergio Santos of the Chicago White Sox grabbed headlines after making the big leagues as a shutdown reliever after struggling for a better part of a decade as a shortstop. Trevor Hoffman also failed as a shortstop before trying his luck as a pitcher. Carlos Marmol played two years as a catcher and outfielder for the Cubs before stepping foot on the mound for good.

It’s not uncommon. One can set foot in a big league bullpen and likely find a former position player lurking in that group — a player that just couldn’t cut it as a professional ballplayer at their respective positions — but the organization saw a special arm they wanted an opportunity to refine on the mound.

In 2011, the position-player-turned-reliever that firmly burst onto the scene was right-hander Kenley Jansen of the Los Angeles Dodgers.

The native of Curacao started as a 17-year-old catcher in the Dodgers’ farm system. He hit .292/.331/.425 in his first professional season, but his numbers dropped significantly in subsequent years. In the end, his career .229 average and .647 OPS simply weren’t good enough, and Jansen faced the prospects of becoming an A-ball journeyman with no more big league dreams.

Then, the Dodgers handed him a baseball, told him to step on the mound, and realized they hit the jackpot when he started to throw 93-94 MPH fastballs past almost every opposing hitter in the minors. Jansen rocketed through the minor league system in only two years — struggling with command at times as he learned the intricacies of being a professional pitcher, but that’s to be expected from a guy who had never pitched before halfway through the ’09 season.

Fast forward to this past year. Kenley Jansen enjoyed his second cup of coffee with the big league club — though technically his true rookie season — and did nothing but break the single-season strikeout rate record. He struck out 16.1 batters per nine innings, and that is the highest strikeout rate in baseball history amongst pitchers with at least 40 innings pitched in a season.

While that is an amazing accomplishment in itself for a rookie reliever, it’s even more noteworthy when one realizes just how it was done. The former record holder, Carlos Marmol, gets a myriad of hitters to swing-and-miss on the strength of his wicked slider; a slider is a swing-and-miss pitch. That makes sense. Eric Gagne (third-best single-season strikeout rate) struck out a ton of batters with a plus-plus changeup. Another swing-and-miss pitch.

Kenley Jansen struck out 16.1 batters per nine innings almost exclusively with his fastball. He threw it 86.8% of the time, and only five relievers in the league had a better fastball, according to the wFB rankings.

Throwing the fastball that exclusively can lead to problems on the mound. The opposing hitter knows what pitch is coming, and big league hitters can turn on any fastball if they can sit dead-red at the plate.

Except Jansen’s fastball, apparently.

The 24-year-old not only threw approximately 87% fastballs in 2011, but he also filled up the strike zone. Only relievers Matt Belisle, Octavio Dotel, and Matt Capps threw more pitches inside the zone than Jansen. So opposing hitters knew which pitch he was going to throw and knew that it would more than likely be within the strike zone, but opposing hitters still struck out 44% of the time.

Turns out opposing hitters simply cannot make contact with his fastball. Of qualifying relievers, only Craig Kimbrel posted a lower contact rate (63.4%) than Jansen (63.5%) — and Kimbrel accumulated those numbers through the use of his phenomenal slider, which he threw 30.5% of the time.

Jansen routinely sits 93-94 MPH with his fastball, but can dial it up to 95-97 MPH with regularity. The pitch explodes on hitters and even has some ride to it as it reaches the strike zone. It’s a straight-up nasty pitch that will only improve in effectiveness as he continues to learn how to be a pitcher and further develops his slider — which is a true, two-plane slider, but lacks consistency.

It’s incredible to that just three seasons ago, Jansen was a little-known catching prospect who was hitting .198/.256/.276 in the California League and was faced with the decision of whether he wanted to transition to a relief pitcher or be released from the Dodgers organization.

Now, despite the fact that Javy Guerra will likely begin the season as the Dodgers’ closer in 2012, the most dominating reliever in Los Angeles before the year is over will probably be Kenley Jansen.

J.P. Breen is a graduate student at the University of Chicago. For analysis on the Brewers and fantasy baseball, you can follow him on Twitter (@JP_Breen).

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12 years ago

Now this is a cool story bro.