Richards sent to bullpen.

MIAMI —Commanding a strong contingent of young starters, the Miami Marlins have developed a good type of problem: having too many pitchers and not enough space in the rotation.

With promising arms waiting in the wings, that means a little less leeway for players suffering through rough patches on the mound.

Dealing with a career-worst stretch in which he’s posted a 7.36 ERA in his past seven starts, the Marlins have moved Trevor Richards to the bullpen. Righthander Elieser Hernandez, 24, will take his place in the rotation, beginning Sunday versus the Arizona Diamondbacks.

In his second major-league season, Richards is 3-12 with a 4.62 ERA and 1.39 WHIP in 20 starts. His 4.05 walks per nine innings is the fifth-highest among qualified National League starters.

After a solid start to the season, the 26-year-old right-hander has struggled in his past seven outings. His 7.36 ERA is the highest among NL starters during that stretch.

“Trevor has obviously struggled a little bit lately, but it gives him a chance to get a little bit of rest [and] also to see what he looks like out there,” Marlins manager Don Mattingly said. “We know as an organization that we keep piling — starters are getting closer and closer to the big leagues.

“There’s been talk early on, ‘This guy could be a really good bullpen guy,’ so it’s the time right now with the combination of Elieser and him to see what he looks like.”

This season, the Marlins have used one of the youngest starting rotations in baseball.

Miami began the season with threesecond year players (Richards, Caleb Smith and Pablo Lopez) and one rookie (Sandy Alcantara). Following injuries to Jose Urena, Lopez and Smith, rookie right-handers Zac Gallen and Jordan Yamamoto, along with Hernandez have shown promising flashes in fill-in duty.

After being promoted from Triple-A New Orleans, Hernandez made five starts, notching a 4.12 ERA and impressive 5.33 strikeout-to-walk ratio (32 strikeouts, six walks). The 24-year-old right-hander transitioned to the bullpen after Smith returned from the injured list.

As for Richards, most of his struggles have come from the inability to develop a consistent third pitch. He has one of the most effective changeups in baseball that’s paired with a decent low-90s fastball. Throwing those two pitches 80.5% of the time, teams are hitting .204 versus the changeup and .261 versus the four-seamer.

Teams have teed off on Richards, though, when he utilizes his secondary pitches. His cutter has yielded a .349 opponents batting average and his curve a .407 mark. Without a strong third pitch, players can more easily ambush his changeup and fastball.

“I think [moving to the bullpen] allows [Richards] to use his two best pitches more often and in short looks,” Mattingly said. “Trevor’s had his biggest issues for the most part getting through lineups multiple times.”