The Mariners’ bullpen might be good enough

If the Mariners are to have one weakness, it’s their starting rotation. The Mariners, in fact, have several weaknesses, but their starting pitching happens to be the most glaring one. Currently, they stand 1.5 games back in the American League Wild Card race. While the Astros have the rest of the AL West in their rearview mirror, the rest of the American League is in disarray. Just three American League teams are no longer in the playoff picture.

The Mariners know they sorely lack competent starting pitchers, which is why they went out and acquired starting pitchers Marco Gonzales and Andrew Albers. Neither Gonzales nor Albers are first-class starters, and so they acquired 1B Yonder Alonso and RP David Phelps to shore up other areas of the roster.

Alonso adds even more punch to an offense that ranks #6 in the MLB in wRC+ (Weighted Runs Created Plus). More relevant is that David Phelps was acquired to bolster the bullpen. Phelps instantly is penned in as one of the M’s best relievers. With the Mariners’ current rotation, the bullpen will be relied upon heavily to backpack them to a Wild Card spot. This is already evident as their 51.1 IP in August is the third highest in the MLB. If the Mariners were to theoretically make it into the playoffs, it is of even more importance that the bullpen has arms that can be confided in in high leverage situations.

The question, then, is if the Mariners have those relievers. Last year, Edwin Diaz was that reliever. This year, while he’s still flashed elite stuff, he’s also been outright atrocious at times.

Nick Vincent currently owns a 6.93 K/9. Not terrible, but certainly below average. Vincent has been striking out less hitters than ever before, but he has also walked fewer, given up fewer home runs, and limited hitters to a 2.01 ERA (2.67 FIP, 4.49 xFIP).

In January, Jeff Sullivan wrote an article about how Nick Vincent had the second most unhittable fastball in baseball in the PITCHf/x era, right behind none other than Aroldis Chapman. Seriously. Ahead of Craig Kimbrel, Dellin Betances, Kenley Jansen, and Andrew Miller. Everyone but Aroldis Chapman. In 2016, he actually had the most unhittable fastball.

Many of these pitchers have fastballs that are either blazing fast or have wicked movement. Amazingly, Vincent’s heater falls into neither of those categories. It averages 90 mph and tops out at 92 mph. As for movement, Brooks Baseball has the following:

His fourseam fastball generates a high number of swings & misses compared to other pitchers’ fourseamers, results in more flyballs compared to other pitchers’ fourseamers, has slightly below average velo and has slightly less natural movement than typical.

In other words, Vincent should have a very ordinary fastball. But he doesn’t! His fastball is elite because he locates it accurately and consistently, has a deceptive delivery, and lives up in the zone with his four-seam fastball. Living up in the zone generally means lots of whiffs and lots of long fly balls. In 2016, those fly balls gave Vincent a 1.64 HR/9, but in 2017 he owns a 0.37 HR/9. One thing we know is out of all types of batted balls, home runs are the noisiest. What that means is home run rates often fluctuate, and what we have seen between the two years is a lot of fluctuation. Nick Vincent was by and large, very unlucky in 2016. This year, he seems to have had a lot more luck on his side.

One of my favorite metrics is a newer one made available by Baseball Savant, xwOBA (Expected Weighted On-Base Average). What it does is take Statcast data and assign hit probabilities to all batted balls. In this way, you can more accurately gauge a player’s true performance and compare it to their actual performance. In this way, you can see how lucky (or unlucky) they have been.

Nick Vincent currently has a .250 wOBA. (Think of wOBA on the same scale as on-base percentage.) His xwOBA is .287.

Hypothesis confirmed! Nick Vincent has benefited from good luck (and similarly good fielding) Using this metric, I can even attempt to say just how lucky he’s been. By subtracting his wOBA from his xwOBA, Vincent has performed 0.037 better than expected. Only six relief pitchers have overperformed more than Vincent. Still, Vincent is still in good company. By xwOBA, Vincent is performing around the level of the likes of Alex Colome, Carl Edwards Jr., and Seung Hwan Oh.

For the sake of (your) time, I will say that David Phelps has been just slightly worse than Vincent has been (which is still good!).

The standout pitcher from the Mariners’ bullpen this year will surprise you. It shouldn’t surprise you, but it will! When you look bad in a couple outings – and I mean bad – people will take a narrative and run with it, and apparently that has been done this year with Edwin Diaz.

Sugar ranks #26 in xwOBA at .258, while his wOBA stands at .282. This means, unlike Vincent, Diaz has not only not but lucky, but he’s been unlucky!

He’s walking just about everybody and he’s given up too many dingers, but since the arbitrarily chosen date of May 19th, Diaz has an FIP- of 74 (100 is league average) while his FIP- on the year is 95. Several of the advanced metrics available expect Diaz to be worse than his current 3.40 ERA is, but there is reason to believe the opposite: that Diaz hasn’t gotten a fair shake due to some bad luck.

Still, this is not the Edwin Diaz of last year, and it certainly seems like something is off. Diaz was probably not going to repeat his insane 2016, but there haven’t been many times this year where he has mirrored that sheer dominance.

One thing is clear: his command is not completely there. From what I can gather via Brooks Baseball, both his vertical and horizontal release points are not in line with where they were last year, and so he’s not locating. Most notably, he’s locating his slider lower than ever.

Diaz is living in the zone far, far less. When you have a slider like he does it can work, except this year both the swing percentage and whiff percentage have gone down on his slider. Diaz has got to get his fastball going or he is going to continue to walk around his rate of 4.56 BB/9. Why swing in the dirt when you can just look for his fastball?

Given this, in the bottom of the ninth of a must-win game: give me Diaz. Vincent and Phelps make for good options, but Diaz by far has the most firepower and was one of the best relievers in baseball last year. He still has until October to return to form.

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