HOUSTON -- Bob Melvin's bullpen pieces are in flux these days.
The A's manager is continually trying to concoct a winning formula, a process that can be experimental at times when multiple arms are struggling.
Right-handers Chris Hatcher and Emilio Pagan, who were expected to play integral late-inning roles at the start of the season, have fumbled of late. Right-hander Santiago Casilla, meanwhile, has quietly delivered consistent results and could subsequently find himself in more high-leverage situations.
"Maybe a little bit ahead of some other guys that at the start of the season wasn't," Melvin said of Casilla, "but we still feel like these guys are talented guys, they're just having a tough time right now."

Hatcher has allowed runs in four of his nine outings for a 9.82 ERA. He held the Astros scoreless in the fifth inning of Saturday's lopsided loss but issued three walks. Each of Hatcher's previous eight appearances came in the seventh inning or later.
"We're trying to give him a couple of different outings just to kind of take the pressure off and figure some things out," Melvin said. "He's had some struggles. We're still kind of in that process at this point.
"It's a tough one to pinpoint. Maybe not throwing as many strikes as he did and certain parts of the zone he's commanded before, he's having trouble with right now. But we feel like he'll get that back."

Pagan, too, has stumbled. The A's sacrificed young slugger Ryon Healy in a trade with Seattle to acquire the right-hander this winter, and he entered Sunday's series finale in Houston with a 5.93 ERA with four home runs allowed in 13 2/3 innings -- accounting for 22 percent of the 18 long balls yielded by Oakland relievers this season, which is tied with the Angels for most in the Majors.
As a rookie with Seattle last year, Pagan surrendered seven homers in 50 1/3 innings, pitching to a 3.22 ERA.
"It's about just getting him confident and back in the roles that we envisioned early on in the season for him," Melvin said.

Like Casilla, rookie Lou Trivino -- excellent in the early going of his career -- could also see more action in the later innings behind closer Blake Treinen and right-handers Ryan Dull and Yusmeiro Petit. Trivino has not allowed an earned run in four outings (5 2/3 innings), while Casilla has given up just two in 10 innings. Opponents are hitting .065 against him.
"He's really done a nice job," Melvin said. "For a guy that's used to pitching a lot and pitching in a certain part of the game, he's had to acclimate to a different role, and he's done it beautifully. Based on need, we closed with him the other night because of experience, but he's had to figure out a way to keep himself ready. I think it comes down to the fact that he just loves to pitch. He'll pitch in any roles, and he's been terrific."