Minor was quietly a dominant arm in 2017

The Rangers have signed free-agent pitcher Mike Minor to a three-year deal, continuing their pitching overhaul. Texas already signed Doug Fister to a one-year deal in late November, and it is currently one of the finalists to sign Japanese superstar Shohei Ohtani, too, hoping to reinforce a rotation that can currently rely on only Cole Hamels and Martin Perez.
Minor is an interesting case, because if you were to simply look at his career numbers, you might not be impressed. After all, a 44-42 record and a 3.93 ERA don't exactly shout "stardom," and he pitched zero Major League innings in 2015 and '16 after injuring his left shoulder pitching for Atlanta in '14.
But we know that career numbers tell you more about what a player has been and less about what a player will be, and if you look at the work Minor gave the Royals in 2017, you'd find a different story. After two years out of the game, he was legitimately one of the best relievers in baseball last year. Texas plans to use Minor as a starter in 2018, as he was with the Braves from 2010-14. We'll get back to that in a second.
The surface-level stats (2.55 ERA, 88 strikeouts in 77 2/3 innings) are a good start. The advanced stats (2.62 FIP) back that performance up. But it's the Statcast™ metrics that really show just how good Minor was in 2017 -- by the most advanced metric we have, Minor was a Top 10 reliever last season.

The way we measure that is with expected wOBA (or xwOBA), which sounds complicated, but really isn't. It measures two things, the two most important things a pitcher can do. First, it looks at strikeouts and walks, or amount of contact; second, it looks at the usual outcomes of batted balls using exit velocity and launch angle, or quality of contact. Then, it expresses that with wOBA, which is basically on-base percentage, except with more credit given to extra base hits. The 2017 Major League average wOBA was .327.
There were 254 pitchers who faced at least 100 batters as a reliever. If you look at the top 10, you will see a list of baseball's most dominant relievers -- and Minor right in the middle.
2017's top relievers by expected wOBA (minimum 100 batters faced)
.198: Kenley Jansen
.216: Pat Neshek
.217: Sean Doolittle
.232:Craig Kimbrel
.233:Andrew Miller and Roberto Osuna
.234: Tommy Hunter
.238: Minor
.240:Chad Green and Brandon Morrow
How? In large part, it's because of the familiar story when a starter moves to the bullpen: Minor's velocity played up, and he was able to drop the pitches that didn't work as well.
Consider Minor's fastball, for example. As an Atlanta starter, he consistently sat in the 91-92 mph range. As a reliever with Kansas City, Minor averaged 94.9, topping 96 mph 48 times -- and reaching as high as 97.2 mph in September. After striking out between 19 and 23 percent of hitters as a Braves starter, he whiffed nearly 29 percent with the Royals.

Mike Minor was a starter from 2010-2014, and a reliever in 2017... in case his fastball velocity chart didn't make that clear. pic.twitter.com/SDfddUDimG

— Mike Petriello (@mike_petriello) December 5, 2017

Not only was Minor's heater coming in faster, it was coming in with a great deal of spin. His four-seam spin rate is 2,604 rpm, which is elite; of the 576 pitchers who threw at least 50 four-seamers, Minor's spin rate was fourth highest, and well above the 2,255 rpm Major League average. High fastball spin can allow the pitch to defy gravity for slightly longer and create the "rising fastball" effect, which can often lead to swinging strikes and popups. Minor allowed just a .210 average on his fastball.
When he was a starter, Minor threw, at times, five pitches -- a four-seam fastball, a two-seam fastball, a curve, a slider and a change. But as a reliever, he primarily became a four-seam/slider pitcher, with those two pitches comprising 80 percent of his pitches, and the slider was effective. Batters hit just .176 against it; no regular lefty reliever threw their slider harder than his 88.5 mph.
Now, can Minor maintain that if he returns to the rotation? In some sense, it depends on what that means. If he's expected to be a traditional starter, getting into the seventh inning, he will almost certainly need to use more than his two best pitches, and it's probable that his velocity could decline. But we know that's not necessarily how starters work these days; it's possible, given Minor's track record, that shorter, more productive starts are acceptable.

Set to return to the rotation, he'll be doing something relatively unusual, in that he'd have been a starting pitcher, then a reliever, then back to the rotation. Over the past two decades, only seven pitchers have done the same, which we'll define as having one season of at least 25 starts, then a season with at least 50 relief appearances, then another season of at least 25 starts.
Those seven were Ryan Dempster, John Smoltz, Kelvim Escobar, Miguel Batista, Jamey Wright, Kent Bottenfield and Danny Darwin, but Smoltz may be the most comparable, spending four very good years in relief after missing all of 2000 due to injury. Minor isn't Smoltz, but it's a transition that's at least possible. It's just difficult to see Minor being as strong in the rotation as he was in relief, as Royals GM Dayton Moore said last month.
"Even if Mike isn't as dominant as a starter -- and he could be dominant, he certainly can -- you know you'll get dominance from him in the bullpen as a one-inning guy or two-inning guy," said Moore. "He's proved it."
Moore wasn't wrong on that. Minor did prove it in 2017, even if six wins and six saves aren't the traditional numbers you'd expect. What we know is that Minor has the talent to make a big difference for the Rangers, and that's exactly what Texas is signing up for.