Adam Warren, David Phelps, and the path of a pitching prospect

After debuting on the same 2012 Yankees team, hurlers David Phelps and Adam Warren revealed the news of their retirements on the same day. There was seemingly no coordination between the pair, who were teammates for five years including their time in the minors.

While they likely didn’t plan to publicly walk away on the same day, the two northpaws undoubtedly shared intel and tutelage on their way through the Yankees’ minor-league system and as members of the Bombers’ major-league staff. Additionally, both started all or nearly all of their minor-league appearances but spent time as swingmen and ultimately full-time relievers in the majors. Put together, the duo represents the challenges of undertaking different pitching roles over the length of a career and hints at what might be done to make things a bit easier.

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To begin their careers though, Warren was arguably more hyped, drafted 10 rounds prior to when Phelps was the year before, the fourth compared to the 11th. But even though Warren had a dominant (56.2 innings, 68.6 GB%, 5 K/BB ratio, 1.43 ERA) short-season debut in 2009, Phelps had an extra season of his own dominance under his belt already (223.2 IP, > 52 GB%, 3.55 K/BB ratio, 2.49 ERA).

So, the first time that both Phelps and Warren were ranked by Baseball America (heading into 2010), the former placed as the Yankees' 25th-best prospect while the latter ranked 26th. After another pair of excellent showings in 2010, the duo climbed the ladder. But with more confidence in Warren after making it through his first professional season, Baseball America bought into his draft pedigree, ranking him 12th and Phelps 16th. Heading into their debut 2012 season, the two lost some ground to fresh-faced breakouts, but Warren remained ahead of Phelps, this time ranking 15th to his 21st.

However, FanGraphs’ Marc Hulet was higher on both, especially Phelps, who ranked 12th to Warren’s 14th. Fascinatingly, Hulet wrote that he chose Phelps over Warren due to Phelps’ greater purported likelihood of remaining a starter. Phelps’ fastball sat low-90s while Warren could dial it up to 94, but the former had a deeper, four-pitch mix. Warren’s unpolished secondaries pegged him for relief duty so that he could focus on refining just one of his lesser offerings in order to achieve a two-pitch combo.

These predictions proved remarkably accurate. Phelps ended up making 67 MLB starts while Warren notched just 21. As a full-time reliever during his last three years in the majors, Warren finally became a two-pitch pitcher. During this span, his slider became that trusty secondary he needed, and he utilized it 45.2 percent of the time after using it at just a 28.1 percent clip across his career prior.

Warren’s four-seamer usage also jumped, going from 31.6 percent to 37.1 percent; all told, he turned to his two favorite offerings 82.3 percent of the time in his last three seasons. Combined, Statcast has them saving Warren 13.5 runs over that stretch.

Despite having the more powerful fastball early on, however, Warren’s ended up flaming out first. Sandwiched between a long-relief season in 2013 and a swingy role in ‘15, the righty pitched as a short reliever in ‘14 and averaged 94.3 mph on his heater, a career-high for the 26-year-old. Yet, he’d never again reach such heights. Understandably, his velocity went down as a swingman in 2015, but even as a full-time reliever again in ‘16, he only averaged 92.9. His velocity gradually dropped until it reached 91.4 in 2019, his last season in the bigs. He tried to salvage his two-pitch repertoire by re-integrating his changeup at the expense of his heater, but at that point, it was too late: the righty limped to a 5.34 ERA and lasted just 28.2 innings in his sole season for the Padres. All of the four-seamer, slider, and changeup cost him runs this time around.

Phelps, the supposedly stickier starter, had a different career trajectory. Over his first four seasons, all but the last with New York, he started 59 of his 110 appearances, firmly in swingman territory. After using him in this role for one season, Miami transitioned Phelps to relief in 2016. His velocity jumped three ticks to 93.6 mph, outpacing Warren that year already. The next year, it ticked up again to 94.7. After missing all of 2018 due to Tommy John surgery, Phelps returned for some of 2019 with dimished velo at 92.7, but rebounded in 2020 with a 94.2 mark and remained above 93 for the rest of his career.

Phelps was the better overall pitcher, his deep repertoire enabling him to put up a 4.29 ERA in 411.1 innings during his swingman years and his velocity propelling him to a 3.05 ERA in 271.1 innings during his relief years. Warren was good in his one swingman year (2015), putting up a 3.29 ERA mark in 131.1 innings, but the rest of his relief-heavy career and later struggles don’t inspire much confidence in that single swing season. Post-2015, he put up just a 3.72 ERA in 203 innings. Overall, Phelps out-WAR’d Warren by a greater than two-to-one margin, and I’d prefer him over Warren in any role.

Though Phelps’ repertoire was better suited to starting than Warren’s, the former’s velocity played up more and stayed that way. Maybe Phelps’ more consistent role year-over-year enabled this velocity consistency; Warren’s heater followed the arc of Joba Chamberlain’s after the latter’s own failed experiment with starting. At the same time, Warren’s move to the pen allowed him to scrap his weaker secondaries, but Phelps didn’t need to be in the ‘pen for this reason: he maintained a four-pitch mix throughout his relief days, with no pair of pitches exceeding a usage rate of 61 percent.

There was ultimately a reason for each hurler to move to the ‘pen. Most pitchers will see some degree of stuff play up as a result of such a move; it’s easier to predict which pitchers based on repertoire, but sometimes, pitchers like Phelps will surprise you with much better velo. Thus, it’s usually worth moving a struggling starter to the pen; just don’t shift their role back and forth much after that.