The Most Important Red Sox Might Be the Middle Relievers

On the surface, the Red Sox and Indians series is somewhat evenly matched. The Indians won 94 games, the Red Sox won 93, and that one-game difference gives Cleveland home-field advantage for the ALDS. But if you look at our Playoff Odds page, our forecasts give the Red Sox a 60% chance of winning this series, because the Red Sox are quietly a monster in waiting.

They had the best offense in the AL this year, and by a laughable margin.


With an offense that dominant, the pitching staff just needs to be okay, and that’s mostly what the Red Sox staff was this year. They weren’t great, but they were solidly above average, and that’s why the Red Sox outscored their opponents by 184 runs, the second-best total in baseball. The Sox pitching staff was strong up front but weak at the back end, as their collection of No. 4 and No. 5 starters all struggled, but that’s the kind of weakness that is downplayed in the postseason. And with more emphasis on bullpen usage in the playoffs, a couple of those struggling starters could turn out to be incredibly valuable for the Red Sox this October.

Joe Kelly, who has had a rough couple of years as a starter, was finally converted into a reliever this year. See if you can spot where it happened in his monthly splits.

Joe Kelly, Monthly Splits
Mar/Apr 50 14 10 11 0.359 0.500 0.632 0.472
May 52 10 6 15 0.222 0.327 0.432 0.327
Jun 17 7 3 1 0.500 0.588 0.833 0.548
Jul 16 4 2 1 0.286 0.375 0.500 0.372
Sept/Oct 53 9 3 20 0.180 0.226 0.240 0.210

After getting beat like he stole something for the first four months of the year, the Red Sox sent Kelly to the minors in August, let him begin to work as a reliever, and then brought him back in September when rosters expanded. And after getting back to Boston, he was one of the best relievers in baseball during the final month of the season.

Unlike most starter-to-reliever conversions, the big jump in success didn’t come from a spike in velocity; Kelly already threw really hard, and he didn’t throw appreciably harder out of the bullpen than he did in the rotation. Mostly, he just started hitting better spots. Look at Kelly’s heat map of pitch selections for his career, and then look at September.



If you want to know why a guy with good stuff hasn’t been a good pitcher yet, that first graph should tell you all you need to know: he lived in the center of the strike zone, where hitters could square up his fastball and drive it to the moon. But look at what he did in September. He got his pitches up and started living at the top of the zone, and if there’s one sure way to get strikeouts, it’s to throw hard fastballs up. As a starter, Kelly was always a pitch-to-contact ground-ball guy, but in September, he was a guy who missed bats by living up in the zone.

This version of Joe Kelly could be an important part of the Red Sox bullpen, giving the team a power right-handed arm to bridge the gap between the starters and the late-inning relievers. Especially with David Price and Eduardo Rodriguez penciled in to start Games Two and Three, Kelly could be useful following the left-handers in Boston’s rotation. Don’t be surprised if the Indians end up seeing a good amount of Joe Kelly in this series — and if he pitches the way he did the final month of the season, they will be sick of him by the end of the ALDS.

Of course, the Red Sox already have a number of good right-handed relievers, so Kelly just gives them extra depth there. What they don’t have a lot of is good left-handed relievers. But after Drew Pomeranz proved sufficiently healthy to stick in the team’s rotation, the team used him out of the bullpen right before the season ended. Here’s a velocity graph from Brooks Baseball, which makes it clear where the relief appearance happened.


In that one outing, Pomeranz topped out at 96, after having mostly maxed out at 93-94 as a starter. He struck out two of the five batters he faced, and looked like a legitimate weapon for John Farrell in October. And we’ve already seen Pomeranz work as a pretty nasty lefty reliever before.

Last year, in Oakland, the A’s converted Pomeranz to the bullpen, and watched him turn into one of the best left-handed bullpen guys in baseball. As a reliever in 2015, Pomeranz allowed opponents to hit just .199/.279/.308, and was especially nasty against LHBs, holding them to a .139/.236/.258 mark. In his career, he’s faced 111 left-handed batters while pitching in relief, and those batters have managed a .212 wOBA against him.

With a big knockout curveball and a fastball maybe now sitting around 95, Pomeranz is a rough matchup for any left-handed hitter. Along with Kelly, he could give the team two starter-conversion relievers who could be highly effective in the middle innings, and allow the Red Sox to not have to lean too heavily on their starting pitchers. And with the Red Sox offense likely to be a wrecking ball in the postseason, the addition of two extra quality bullpen arms could make Boston a very tough October opponent.

The Indians are a also good team, of course, and in the postseason, anything can happen. But with Kelly and Pomeranz looking like potential weapons out of the bullpen, in addition to all the other good players they already had, the Red Sox look like the kind of team built for a strong postseason run.

Dave is the Managing Editor of FanGraphs.

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6 years ago

Another big problem Kelly had was that he got very predicable which you can’t get away with when you’re going through the lineup 2-3 times but you can get away with it when you only face a couple of batters. That and he seemed way too fond of his 2-seamer which had almost too much movement and it would leak back into the middle much too often.