One Big Question: Can Joe Kelly dominate in a full season of relief?

Welcome to Over The Monster’s One Big Question series. For the next 40 (week)days, we will be trying to answer one important question for each player on the Red Sox 40-man roster. The goal is to find one interesting portion of each player’s game to watch for, whether that be in spring training or the early regular season. We’ll be going straight down the list on the team’s roster page, meaning we’ll be going in alphabetical order through each position group, starting with the pitchers. Today, we’re highlighting Joe Kelly.

The Question: Can Joe Kelly dominate in a full season of relief?

We all know the story of Joe Kelly’s Red Sox career by now. He was acquired in what was one of the worst trades in recent team history, coming along with Allen Craig in exchange for John Lackey. The team continuously insisted he was a starter, and Kelly struggled in both Boston’s and Pawtucket’s rotation. After roughly two years of speculation that he was better suited for a role in the bullpen, the team finally put him in relief midway through the 2016 season. He spent much of that time in Pawtucket’s bullpen, getting himself accustomed to his new role, but he did get a month’s worth of work out of the ‘pen with the Red Sox. He looked like an entirely different guy in that small sample, leading to one of the most obvious questions for any Boston player heading into 2017.

As I said, the sample is incredibly small, with Kelly facing just 69 batters in the regular season as a reliever, and 11 more in the ALDS against the Indians. These are the only numbers we have, though, and they hint towards a superior pitcher than the mediocre-at-best righty we’d seen in the rotation. Batters -- who were about 65 percent right-handed — hit .203/.261/.297 against Kelly, good for a .247 wOBA. For context, that was the eighth-worst wOBA among the 353 players who received at least 200 plate appearances last year. He followed that up by retiring all 11 batters he faced in the postseason.

Even better, the peripherals supported those phenomenal results. After striking out just under 23 percent of batters and walking 16 percent as a starter, he improved those rates to 30 percent and 7 percent, respectively, out of the bullpen. Those are elite numbers. In 2016, just seven relievers were able to post those rates over the course of a full season (min 40 IP). Of those seven, the only one who couldn’t undoubtedly be considered elite in 2016 was Koji Uehara, who we all know is still pretty damn good.

Back in October, before he went on his impressive three-game run in the postseason, I looked at Kelly’s run as a reliever and found some changes in his repertoire. Specifically, I noticed that he cut out his sinker and leaned more heavily on his breaking ball. In particular, he utilized his curveball more. This, combined with a fastball that jumped up to an average velocity of just under 99 mph, led to these phenomenal results.

The curveball was a great secondary weapon, as it induced whiffs on exactly a third of swings and ground balls on three-quarters of balls in play. However, it was the fastball that made things happen for Kelly at the end of the regular season. No longer having to hold himself back to make it deep into games, the 28-year-old could let loose and challenge hitters. As you can see, he did just that by heaving high fastballs at his opponents and daring them to hit it.

A good number of the times, he those challenges.

In the postseason, Kelly now-famously invented a “new pitch” just about ten minutes before the first game. In reality, it was just a revamped slider, but it was effective all the same. According to Brooks Baseball, he threw the pitch 42 percent of the time during the ALDS, more often than any other pitch. The 91 mph breaking ball was certainly as effective as he claimed in the linked article, as he induced whiffs on over 40 percent of swings and grounders on half of the batted balls it allowed. If he can carry that pitch, along with the curveball and high-powered fastball into a full season of work, watch out.

The other piece of good news is that, while last year was his first taste of bullpen life with the Red Sox, it wasn’t the first taste of his career. In 2012 and 2013, his first two years in the league, Kelly split the seasons between the bullpen and rotation. In 2012, his opponents’ OPS as a reliever was 116 points below the OPS he allowed as a starter and his K/BB was twice as high. The following year, he actually allowed a higher OPS as a reliever, but the K/BB was just as significant.

It wasn’t all good news for Kelly, though, and there’s still one issue with his game. As someone who has never really developed full trust in the righty, it’s easy to see the issues with his command. Even at his best, he has a tendency to leave balls right over the middle of the plate. He only allowed one home run as a reliever in 2016, but he also saw an increase in fly ball rate and decrease in ground ball rate. Part of that is by design — those high fastballs aren’t exactly a recipe for grounders. That can be a dangerous game for someone with his command issues, though.

Still, that’s not enough for me to talk myself out of believing in Kelly, which is a tough sentence for me to type. I’m not going to say that he’s going to be just as good as he was in the small sample last year, because that would make him an easy top-ten reliever in the game. Still, I expect he’ll work his way into late-inning situations sooner than later. The Red Sox have a solid base at the back of their bullpen with Craig Kimbrel and Tyler Thornburg, plus the return of Carson Smith at midseason. Given the changes we saw from Kelly after shifting to his new role — particularly that new slider he displayed in the postseason — they could have a quietly terrifying back-end of the bullpen that will rack up strikeouts at a ridiculous rate.