Brad Ziegler lives large at the bottom of the zone

In the unpredictable game of baseball, relievers are typically the unpredictabl-est commodity of all. With injuries routinely shortening promising careers, spontaneous implosions, and more specialization within the craft, the shelf life of relievers seems to be shortening.

Of course, there are still the guys who come into the league and stick in the pen, dominating late innings for years and years. Guys like Aroldis Chapman have commanded comically huge returns in trades as the value of a true shut down reliever is hard to overstate. Teams routinely look for pitchers who can shorten games, a skill even more valuable come playoff time.

Over the past decade, one of the most dependable arms in the league has been that of Brad Ziegler. A submariner and FIP beater with a fantastic back story, Ziegler has posted an ERA above 3.00 three times in his nine-year career, never eclipsing the 3.50 mark. How is he still so good all these years later?

He's nearly unhittable at the bottom of the zone and he's getting help from umpires

Every Ziegler offering is loaded with downward movement. It's what has kept him a competent pitcher in spite of rarely missing bats, and his aptitude for ground balls will play especially well in cozy Fenway Park.

This year, Ziegler is throwing by far the lowest amount of pitches in the strike zone, per FanGraphs' Zone%. Of all his offerings, only 38 percent pass through the zone, a number usually indicative of a walk-prone pitcher. How's he getting away with that? He is indeed walking hitters at a slightly higher rate than normal (3.21 BB/9), but more often than not, hitters are being forced to swing at balls out of the zone due to umpires giving Ziegler a generous zone. Here's the average strike zone this year:

And here are the calls Ziegler is getting.

Undoubtedly thanks to his quirky mechanics and extreme downward movement, Ziegler is getting a substantial number of calls below the zone. Notably, neither of Ziegler's primary catchers this season, Welington Castillo with Arizona and Sandy Leon with Boston, has graded out as a particularly good framer by Baseball Prospectus' measure, so this seems to be coming more from Ziegler himself than his receivers.

That's double trouble for hitters, since when Ziegler hits the bottom of the strike zone, hitters are rendered nearly useless. When he's just below the zone? Hitters are handcuffed.

Most of the time, hitters could just take those pitches and be reasonably sure the umpire will call it a ball. Instead, since Ziegler is getting those calls, batters are forced to swing and, the vast majority of the time, either miss or pound the ball into the ground.

Is it all in his mechanics?

It's hard to pinpoint the exact effect of Ziegler's unusual submarine motion. However, we can compare him to a similar pitcher who has seen similar results. Darren O'Day has also been an exceptionally consistent and effective ground ball-inducing sinker-baller and a pitcher who has benefited from a particularly wide strike zone in a particularly convenient place.

There are of course failed sinker-ballers and guys who can't maintain success for more than a short few years. But with Ziegler and O'Day having longer than average careers in the pen with a very tangible advantage over normal pitchers, it's hard not to wonder. Is submarine pitching an underrated art?

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Tim Eckert-Fong is a contributor to Beyond the Box Score.