Just two years removed from pitching in Single-A, right-hander Luis Perdomo is a full-time member of the Padres’ starting rotation. In December 2015, he was selected by the Rockies in the Rule-5 draft and later traded to San Diego for cash considerations, which is the reason for his quick ascension.
Originally signed by the Cardinals as an international free agent in 2011, Perdomo posted a 4.10 ERA in 316 innings across four different minor league levels; none above High-A. But being a Rule-5 pick, he was thrust into the majors in 2016.
He began the season as a member of the Padres’ bullpen, but that proved disastrous for the right-hander (9.10 ERA in 29 2/3 innings), prompting the Padres to transition the Perdomo into a regular role in the starting rotation.
He found much more success there, where he owned a 4.85 ERA and 4.69 FIP in 117 innings. The radical change came as the result of a drastic shift in pitch selection.
In the bullpen, he deployed a very fastball-heavy approach, which is to be expected for a guy with a 95-mph fastball like Perdomo. But the problem last year was that his four seamer just wasn’t very effective; batters crushed the pitch to the tune of a .476 batting average and a .768 slugging percentage and rarely whiffed (5.01%).
When he became a starter, though, he suddenly became more reliant on his sinker than any other pitch. In April of last year, Perdomo threw his fastball a tick over 40% of the time and his sinker just under 12% of the time. By September, though, he had nearly ditched his four seamer altogether, throwing it just 3.6% of the time.
He still used his curveball and splitter about as often as before, but Perdomo’s sinker usage was up to 60% by then, and it quickly became clear that his path to success would be paved by the ground ball.
As a reliever, Perdomo generated grounders at an above average rate of 52%. But as a starter, he increased that to 61.1%, which led all starters with at least 110 innings pitched last year. Also with his move to the bullpen came a slight decrease in strikeouts and walks.
He has carried all of those changes over to 2017 and… produced almost exactly the same result. In 116 2/3 frames this year, Perdomo owns a 4.95 ERA. His pitch selection is nearly identical to what it was in September 2016, and he has continued his extreme groundball tendencies, as his 61.7% GB% sits among the best in all of baseball.
In addition, he is getting batters to swing at pitches in the zone (63.2% this year vs. 64.4% last year) and out of the zone (28.9% vs. 31.2%) as well as swing and miss (9.3% vs. 8.6%) at about the same rates as last season. And lastly, he has fanned 17% of batters as compared to 16% as a starter in 2016, and his walk rate of 8.6% is up marginally from 5.9% a year ago.
So Perdomo’s performance has plateaued. But he’s still just 24 years old, can generate ground balls better than almost anyone in the majors, and has plenty of room for growth.
Like many sinker ballers, Perdomo’s performance hinges on location since he can’t simply blow hitters away with his 88-mph sinker. For instance, the righty’s sinker is dominant when he keeps it on the low corners of the strike zone; opposing batters are hitting just .232 and slugging .285 against the pitch when he does so.
However, he runs into problems when he leaves it up in the zone. When Perdomo’s sinker ends up in the middle of the zone or the upper part of the zone, batters are hitting a sky-high .396 and slugging .631.
Additionally, Perdomo suffers greatly due to San Diego’s poor defense. With so many balls put in play against the 24-year-old, he relies heavily on the defense behind him to help him out. But the Padres have fielded one of baseball’s worst defenses this year; Defensive Runs Saved rates the club as the fourth-worst fielding team in the NL while Ultimate Zone Rating pegs them as the worst.
This has resulted in Perdomo having to deal with the sixth-highest batting average on balls in play among starters. And the 0.56 difference between his ERA and FIP, which can be largely attributed to the inadequacy of his team’s defense, is the 15th-biggest differential in the big leagues.
Perdomo’s 85 ERA+ indicates that he has been a well below league average pitcher this year, but his fielding independent numbers paint a prettier picture. The average NL starter this year has a 4.42 FIP; Perdomo’s is 4.39. And the average xFIP among NL starters is 4.33; Perdomo’s is 4.31.
If Perdomo’s floor is an average major league starter as it appears to be, he will be plenty valuable to the Padres both now and in the future even without additional development. But if he progresses further and refines his command as he gains experience, he could be even better than that. And the fact that he’s only in his age-24 season–with fewer than 600 professional innings under his belt–and has already shown an ability to implement changes and maintain them over an extended period bodes mighty well for the future.