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How Have Notable Relievers Transitioned to Starters?

Current Braves SP Reynaldo Lopez when he was with the Nationals; Photo via UCInternational

For one reason or another, minor league starters are sometimes converted to relievers upon arrival to the majors. Pitchers with elite stuff who would struggle as major-league starters, whether it be due to struggles with command or a lack of a deep repertoire, can reinvent themselves by converting to high-leverage relievers. But what about the other way around? Can relievers effectively transition to being starters? Three former relievers are all trying to make this transition today. 

Michael King, San Diego Padres

Stats through May 6: 42.0 IP, 4.96 pCRA, 24.8% K%, 12.4% BB%, 10.0% Barrel%, 41.7% GB%, 31.1% CSW%, 11.1% SwStr%, 26.4% Whiff/Swing%

Michael King started six games down the stretch for the Yankees last season, and he was very effective, enough to the point that the Padres made him a key piece in their return for Juan Soto. However, King has struggled to start the season. He’s in the 23rd percentile in walk rate, 20th percentile in barrel rate, and 56th percentile in strikeout rate. His struggles ultimately come down to command, particularly of his four-seamer and sinker. As seen in the heatmaps, King is leaving both pitches right down the middle of the zone, resulting in 14.7% and 22.2% Barrel rates, respectively. Looking back from his starts with the Yankees, both pitches have also regressed from a stuff standpoint: They’ve each lost 1.7 MPH of velocity, the four-seamer has lost 0.9 inches of induced vertical break, and the sinker has lost 1.7 inches of arm-side run. Considering neither pitch had elite movement or velocity to begin with, this regression is concerning.

Heatmaps via Baseball Savant

However, there are still pieces of an effective pitcher: His primary offspeed pitches, the changeup and sweeper, are still elite pitches. King uses both to limit hard contact, as neither pitch has given up a barrel yet, and generate whiffs at a high rate, with the changeup at a 41.1% whiff rate and the sweeper at a 28.8% Whiff rate. If King is going to become the pitcher the Padres thought they were getting when they gave up one of the best players in baseball, he needs to stop leaving his fastball and sinker in the heart of the zone. If he can do that, the pieces are there to be a key rotation piece for a Padres team with October aspirations. 

Jordan Hicks, San Francisco Giants

Stats through May 6: 38.0 IP, 4.32 pCRA, 19.7% K%, 8.6% BB%, 6.7% Barrel%, 58.1% GB%, 27.9% CSW%, 9.9% SwStr%, 22.7% Whiff/Swing%

Jordan Hicks was one of the hardest throwers in the game last season with the Cardinals, but the Giants gave him a four-year contract to become a starter. The consensus was that this was risky, especially for a guy who has battled injuries in the past. So far, however, this contract has paid off big time, although I don’t think he’s as good as his 2.30 ERA suggests. One repertoire change that has helped Hicks is increasing the usage of a splitter. He uses it 23.3% of the time this season after using it accounted for under 2% of his pitches last season. It’s his primary strikeout pitch, as he uses it 37.6% of the time in 2-strike situations, and his primary pitch to generate whiffs, sporting a 43.2 whiff%. Jordan’s splitter is prone to hard contact, as evidenced by an 11.8 Barrel%. Hicks’ other offspeed pitch, the sweeper, is also very effective as it plays well off of his sinker and gives him a pitch that moves glove-side. It generates whiffs at about an average rate but is elite at minimizing hard contact, as it has yet to give up a barrel this season. 

Because he’s a primary sinker pitcher, he’ll never be an elite strikeout artist. But if Jordan Hicks can continue to generate groundballs at an elite rate (he’s in the 89th percentile), he can be a great piece in the Giants’ strong rotation behind Logan Webb and Kyle Harrison. 

Reynaldo Lopez, Atlanta Braves

Stats through May 6: 30.0 IP, 3.46 pCRA, 27.0% K%, 8.7% BB%, 5.4% Barrel%, 44.6% GB%, 30.5% CSW%, 14.8 SwStr%, 30.0% Whiff/Swing%

Reynaldo Lopez was actually a starter with the White Sox from 2018-19 before being converted to a reliever, and a pretty good one at that. The Braves signed him this offseason intending to make him a starter. It has paid off so far, especially considering Spencer Strider’s injury. Lopez has been elite at limiting barrels, as he has yet to give one up on both his slider and curveball. The slider, which Reynaldo uses 29% of the time, is his best pitch. He’s added depth to it, and the following impressive results have ensued: 39.5 K-BB%, 1.02 pCRA, 0.0 Barrel%, 61.9 GB%, 31.8 CSW%, 23.3 SwStr%, and 46.2 Whiff/Swing%. His fastball has been elite in limiting barrels, as it has a 4.5% barrel rate, well below the average of 10.1%. However, this might be due for regression, as Lopez’s average exit velocity of 91.1 mph and hard-hit rate of 48.8% on his fastball fall in line with the average for the pitch

Reynaldo Lopez was a shrewd acquisition for a Braves rotation that started the year ravaged by injuries and unexpected struggles. While I doubt Reynaldo Lopez will maintain his 1.53 ERA for the rest of the year, if he can continue to be effective, it’ll go a long way for the Braves to overcome the October demons that have haunted them the last couple of seasons. 


These three pitchers have experienced varying degrees of success. As the season wears on, it’s fair to expect some regression as they adjust to their higher workloads. While King has struggled out of the gate, the other two have proven that the transition from starter to reliever can be effective, although it may come with limited workloads to start the season. With a constant need for starting pitching and the steep price for high-level starters, it should be noted whether teams look to relievers to try to fill out their rotation. 


"Reynaldo López on August 23, 2016" via UCInternational licensed under CC BY-SA 2.0


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