The 2011 Texas Rangers represented the American League in the World Series for the second year in a row, and did so primarily on the strength of their rotation. Of the top five pitchers in games started for the Rangers last season, three of them were converted from relievers to starting pitchers within the last two years. C.J. Wilson was in his second year in the rotation after a successful 2010 campaign, while Alexi Ogando and Matt Harrison were there for the first time, combining for 59 starts and 354 innings pitched. Without those conversions from relief to starting, it's likely the Rangers wouldn't have made it as far as they did in October the past two seasons.
Major League Baseball is a copycat league, and if something works for one organization, you'll start to see it in practice more often. Once again, the Rangers will move one of their relievers to the rotation, but many other teams are following suit with their own powerful bullpen arms. While some transitions might be ill-advised, most of them should be beneficial.
Neftali Feliz has thrown 162 innings for the Rangers over the last three years, and another 276 over four minor league seasons. He was a full-time starter for just one year in 2008, as the Braves split his time between the pen and rotation before that, and the Rangers spent 2009 preparing him for his bullpen role in the majors. He was very successful starting, posting a combined 2.69 ERA across Single- and Double-A with 10.8 strikeouts per nine and a 3.0 K/BB.
He threw 108 innings between Triple-A and the majors in 2007, but has just 131 combined over the past two seasons. Despite three years in the majors, he's still just going to be 24 in 2012, so don't take this as an indication he can never throw 200 innings in a season.
The Red Sox had terrible starting pitching from the last three spots in their rotation in 2011, and they spent most of the off-season collecting fifth starter types off of the scrap heap. Part of the reason they didn't push for the likes of Edwin Jackson, Hiroki Kuroda, and others hard is because they have Daniel Bard. Bard was drafted as a starter, but the Red Sox have used him in relief out of necessity, in the same way the Rangers utilized Feliz.
Bard and Feliz have comparable career numbers (Bard: 154 ERA+, 9.7 K/9, 2.8 K/BB; Feliz: 178 ERA+, 9.1 K/9, 2.9 K/BB), and their three-pitch repertoires are similar, too (blistering fastball, slider, and a change-up mostly used to neutralize left-handers). Tango's "Rule of 17" -- which states that K/PA is up 17 percent as a reliever, BABIP is down 17 points, and home run rate is down 17, too -- unsurprisingly projects this pair out to similar 2012 seasons as starters using their career numbers:
The league average K/PA, home runs per balls in play, and BABIP in 2011 were 18.6, 3.4, and .291 respectively, meaning both of these relievers are expected to be better than average in those categories. If you're wondering why walk rate isn't included, it remains static in the transition -- higher walk rates do cause more damage for starters than relievers, though. The ERA projection comes courtesy of Nate Silver's research:
...the typical pitcher will have an ERA about 25% higher when pitching in a starting role than when pitching in relief. That is, if you take a given reliever with a 3.00 ERA, your best guess, all else being equal, is that his ERA as a starter would be 3.75.
Silver also attempted to figure out how good a reliever would need to be to merit throwing fewer innings than a starter:
Throw all of these assumptions into a blender, and we find that a 2.00 ERA closer is roughly as valuable as a 3.69 ERA, 200-inning starting pitcher.
Neither Feliz nor Bard are that level of closer, despite their obvious talents -- few ever have been. They might, however, be capable of being that hypothetical starter or better, meaning this switch makes far more sense for them than continued bullpen existence.
The White Sox are moving Chris Sale to the rotation, in the hopes of finding similar success. Sale has less of a track record than either Bard or Feliz, as he was drafted in 2010 and then threw 23 innings in the majors the same season. He has struck out batters at an even higher rate (10.6 per nine) and posted a similar K/BB (3.0) in his 94 frames. He has the same mid-90s and better velocity, too, but actually features four pitches: four-seam fastball, slider, two-seamer, and change-up. Despite this deeper (and effective) selection of pitches, Sale has never started a game professionally, but he was a successful starter at Florida Gulf Coast University.
As with Bard and Feliz, the Rule of 17 and Silver's research look kindly upon Sale: 24 percent K/PA, 4.0 HR/BIP, .288 BABIP, and 3.23 ERA. As his career-high in innings pitched was 103, and that was back in college, the White Sox might need to be careful ratcheting up the 23-year-old's workload, but otherwise this looks like a great plan for both Sale and Chicago.
Aroldis Chapman's situation is a little less clear-cut. Chapman has been great as a reliever, like the others, but the bullpen has also hidden some of the damage his obscene walk rates could have caused were he a starting pitcher. He has a career 2.0 K/BB in 63 MLB innings despite walking 6.5 batters per nine, thanks to punching out nearly 13 per nine.
This isn't to say the Reds shouldn't try him there -- his arm has loads of potential, and he was successful in his brief stint as a starter at Triple-A in 2010. He has the same heater, slider, change-up combination that all of these other arms utilize, and his record-setting fastball is at a whole different level. The change in approach that comes with starting -- maybe Chapman won't rear back to try to throw 103 all the time -- might give him better control of his stuff, nixing the potential walk issue, too.
The Rangers have reminded teams that you don't need to sign free agent starters or promote prospects to improve your own rotation all of the time, as maybe you have upgrades you haven't been properly utilizing already. Four other teams might all be better in 2012 for following suit; if that's the case, you'll see the other 25 tag along soon enough.