Santiago is 0-6 with a 5.19 earned-run average. The Angels are 0-7 when he starts and 16-10 when he does not.
The Angels are likely to call up a starter from triple-A Salt Lake to take Santiago's next turn, scheduled for Tuesday in Philadelphia. The Angels also sent left-handed reliever Sean Burnett to double-A Arkansas to begin a rehabilitation assignment that could last the maximum 30 days.
For now, Santiago is the lone left-hander in the bullpen. The Angels informed Santiago of the move Friday afternoon, before the team opened a four-game series against the Toronto Blue Jays.
"They said, 'You're going to the bullpen.' That's it," Santiago said. "It was short and sweet, and to the point. Obviously, I didn't want it to happen. I've been kind of looking for something to happen, the way it was going."
Santiago has failed to pitch six innings in five of his seven starts. In his last start, he pitched 2¿ innings, then left the mound before Manager Mike Scioscia arrived to remove him, a breach of baseball protocol for which Santiago subsequently apologized.
Angels pitching coach Mike Butcher said the demotion was “100% not a disciplinary thing" and said the team would like to see Santiago earn his way back into the rotation, provided he can better control his pitches -- he has 18 walks in 35 innings -- and his emotions after a play goes awry.
Said Butcher: "The plan right now is for him to be in the bullpen and help us win games out of the pen, and hopefully clear his head a little bit and get back on track.”
Santiago flourished as a swingman for the Chicago White Sox, with a 3.51 ERA in 23 starts and 3.93 ERA in 11 relief appearances.
"Maybe this will put me on the right path," Santiago said. "Maybe this is where it can turn around."