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Adam Conley the lights-out reliever?

The sample size is still small, but Conley’s adjustments to bullpen life should have batters on the 29 other MLB teams very concerned.

MLB: Miami Marlins at San Francisco Giants
Lots of elbows and knees flying at you, especially as a left-handed batter.
Kelley L Cox-USA TODAY Sports

The Miami Marlins thought they may have found a pretty solid middle-of-the-rotation arm in Adam Conley after the tall, lanky, lefty impressed in his first two major league seasons. From 2015-2016 Conley was solid, owning a 12-7 record with a 3.82 ERA and racking up over 200 innings in 36 starts across the roughly season and a half.

Coming into the 2017 season, Adam Conley shaped up to be a key member of the Marlins rotation. The third-year pitcher expected to shoulder plenty of innings and provide consistency to a Marlins pitching staff that so badly needed continuity. However, in a season filled with disappointment for the Marlins, Conley was among the most troubling. The then-27 year-old pitched to a 6.14 ERA in 20 starts, with a WHIP of 1.52. The Marlins would send Conley down to Triple-A New Orleans to figure things out, but he put up virtually the same numbers against minor league competition.

As a last resort, the Marlins decided to try Conley in the bullpen when he returned to the bigs this past May. That’s where things clicked for the fourth-year pitcher. In 23 23 innings as a reliever, Conley has struck out 29 and boasts a WHIP of 0.89.

So what changed? The short answer: Everything.

Conley’s move to the bullpen has allowed him to put more into his pitches, perhaps even more than the Marlins thought he had in him. The 6-foot-3-inch lefty’s average fastball velocity jumped from 89.5 to 94.9 MPH and the slider jumped over 3 MPH as well. Conley’s dramatic jump in velocity has allowed him to attack hitters more frequently and while setting up his changeup, a pitch he is now using nearly a third of the time. That’s up from 18 percent in 2017.

Adam Conley’s newfound ability to change speeds has showed up in his strikeout rates. Across his last two seasons in the minor leagues, Conley did not break 15.0 K%; in his 23 23 innings as a reliever, that rate has more than doubled to 31.5%. Conley’s jump in punch-outs has helped FIP drop from 5.60 as a starter in AAA this season to 3.47 in his new relief role.


Even when Adam Conley was at his best, he still had a tendency to give up a lot of hits, especially to left-handed hitters. In his two successful seasons as a starter, Conley’s WHIP sat at 1.36 and lefties batted just under .300 off of Conley. For Conley to be an effective southpaw out of the bullpen, reverse splits aren't ideal.

Now, he has completely flipped the script. Same-handed hitters have combined for a minuscule .132 batting average in 2018. Conley’s drastic improvement is largely due to the increased depth and velocity on his slider, a pitch he is confidently throwing nearly 11 percent more frequently to lefties.

Conley’s steep drop-off from his fastball—that can touch 96 MPH—to his low 80s changeup has enabled him to keep righties off balance. The southpaw is throwing them changeups a third of the time. That offering has a Pitch Value of 5.7 per FanGraphs, which ranks among the best changeups in the league (min. 20 IP). He’s keeping good company between Max Scherzer (5.3) and Jacob deGrom (6.1), raising his ceiling well beyond that of a lefty-specialist.

Conley strikes out All-Star Jesús Aguilar on Wednesday.
Fish Stripes original GIF

The Marlins giving Adam Conley one last chance in the bullpen could be a result of the team learning from how the Red Sox handled their former failed starter, Andrew Miller. Miller, who was one of the headline prospects who came from the Tigers in the infamous Miguel Cabrera trade, posted nearly identical numbers to Conley as a starter.

  • Miller, 2008-2010: 220.0 IP, 4.49 FIP, 17.1 K%
  • Conley, 2015-2017: 303.0 IP, 4.59 FIP, 19.2 K%

The Marlins gave up on the once highly touted lefty and shipped him to Boston, where he struggled as a starter as well. The Red Sox eventually moved Miller to the bullpen where the southpaw would thrive thanks to: Increased velocity and K%, improved splits, and increased slider usage. Sound familiar?

Using 2009 as a reference (his final season making more than 13 starts), Miller’s fastball jumped from 90.9 as a starter to 94.9 mph in his breakout bullpen campaign for the Red Sox in 2012. His slider velocity jumped from 77.7 to 82.8 mph and Miller’s slider usage nearly tripled to 39.4 percent. While Miller eventually completely eliminated the changeup from his arsenal, his increased usage and effectiveness of the slider and fastball reflects that of Conley’s, especially to lefties.

Andrew Miller’s increase in K% from starter to reliever was just about identical to that of Adam Conley’s doubling from 16.1 to 30.2 percent, while his FIP dipped from 4.45 in 2009 to 1.51 in 2014. Due to injuries the last two seasons, Miller hasn't quite been as stellar as previous seasons, but the extreme shift from 2009-2013 mirrors that of Conley’s so far.

Tall, left-handed pitchers tend to have more moving parts in their mechanics. It often takes a lot of trial and error for them to find what works mechanically. For Andrew Miller, it was exclusively going out of the stretch. For Conley, he has made various adjustments, including his release point to improve his command.

While the sample size is small on Conley, his massive improvement has come in nearly all of the same metrics that Miller saw jumps in himself. He’s found a second life out of the bullpen, so it’s no wonder the Marlins’ front office phones keep ringing—this newfound dominance looks sustainable.