Kenley Jansen has always been really good, but he's been extraordinary this season.

He took hold of the closer's role in 2012, and he has not let go of it since. Jansen has since set the Los Angeles Dodgers' franchise record for saves, and he's become the only player in team history to have five seasons of at least 20 saves. He has amassed 195 saves from 2012 to date, good for the second-most in baseball in that time frame, behind Craig Kimbrel. His 13.3 fWAR in that span trails only Aroldis Chapman among relievers as does his 1.83 FIP.

Any way you slice it, Jansen has been one of the elite relievers in the game since 2012.

He parlayed his success into a five-year, $80 million contract extension to stay in Dodger blue. The Dodgers paid a premium to retain Jansen's services (something that is likely to become the new norm as relievers are used more frequently), and the move has been nothing but genius so far this season.

A Dominant Campaign

Jansen has put up video-game numbers this season. He has faced 107 batters and surrendered a meager 17 hits. In 29 2/3 innings, he has allowed 4 runs, only 3 of which are earned -- good for an 0.91 ERA (and ERA- of 22).

He is near the top of the reliever leaderboards in pretty much every meaningful statistic.

The thing that pops out, obviously, is the walk rate. It's zero. Yup, in 29 2/3 innings and 107 batters faced, he has yet to surrender a walk. In fact, Jansen has only had nine three-ball counts this entire season.

He is pounding the zone at a monster rate -- his first-strike percentage is a whopping 79.4%, up from a career average of 64.9%. The highest single-season first-strike percentage he had prior to this year was 69.5%. He was always above-average with his command, but this year he has been on another level. He is blowing away the league-average first-strike percentage of 59.3%.

Maybe one of the most surprising things about the table above is that Jansen is not the clear-cut leader in every category among relievers. That's thanks to Kimbrel, and his equally ridiculous 2017 campaign.

While Jansen's numbers look positively fictional, his xFIP seems to be an odd outlier, but it is actually due to the kind of pitcher he is. Dating back to 2015, Jansen has been an extreme fly-ball guy. He has posted fly-ball rates of 53.7%, 54.6% and 51.8% over the last three seasons. He has coupled that with an ability to stifle home runs, especially in the last two seasons -- his home-run-per-fly-ball rate was 5.6% last year, and it is 3.4% this year.

xFIP expects him to regress to the league-average in terms of home runs allowed, especially with his elevated fly ball numbers. However, his FIP and xFIP were a run apart in 2016, as well, so he has a history of outperforming his xFIP.

He Has Actually Been a Little Unlucky

Despite his impressive performance this year, Jansen has actually been a bit unlucky in some respect, and his numbers should possibly be even better than they have been.

Saying that someone who has yet to surrender a walk while only giving up three earned runs should have even better numbers sounds a little absurd. However, he is currently sitting at a BABIP of .291, good for 99th among all relievers and up from a career .273 number.

When batters actually get their bat on the ball, they have been moderately successful at getting hits, even though they should not be. His hard-hit rate is a lowly 19.6%, and fly ball pitchers are more likely to have low BABIP's because of the nature of fly balls -- it is a lot easier to beat out an infield single, or sneak a grounder past two gloves, than it is to have a blooper fall in for a hit.

Jansen's profile lines up with someone who should have a low BABIP, but he has given up more hits than normal. This is not the first time he has had an elevated BABIP -- in 2014 he ended the season with a whopping .350 BABIP, though he was not the fly-ball pitcher he has turned into these past two seasons. In 2016, the first year he started to generate an insane amount of fly balls, he had a BABIP of .238, which is much closer to where he should be this season.

One Special Pitch

Jansen's success stems from one (amazing) pitch -- his cutter. In 2017, he has been throwing it 91.2% of the time, which would break his career high of 89.7% from last year. He relies heavily on this offering, and for good reason -- it is an excellent pitch.

Above, we can see of the movement of his cutter, thrown during this past World Baseball Classic. On average, he has uncorked his cutter at a speed of 93.4 miles per hour in 2017. A pitch that fast shouldn't be able to move that much, and it goes a long way toward explaining why he has been so hard to hit this season. If he locates it correctly (and his 0.0% walk rate is an example of his control), the pitch is basically unhittable.

While he does rely on it to an extreme level, he changes the way he approaches the batter in order to keep them off guard.

In one at-bat, he approached the hitter in three different ways. Even if he throws the same pitch three times, the deviation of his approach would throw off the hitter regardless.

Kenley Jansen is a pitcher at the very top of his game. He has perfected his cutter, and it has helped him become one of the two best relievers in baseball. Not only has he been an elite reliever, there are only 14 starters who are more valuable than he has been this season in terms of fWAR. Jansen has been a game-changer at the back-end of the Dodgers bullpen, and there are no signs of him slowing down.