But in his last three outings, Marmol has served up home runs, including one on Thursday to San Francisco pinch-hitter Rich Aurillia in the Cubs' 8-3 loss.
"He's throwing some fastballs up," Rothschild said Friday. "That's been the biggest thing. He's going through one of those periods where every bad pitch is being hit, and hit hard. I think he'll get through it. He's got too good of stuff."
There's nothing physically wrong with Marmol, and he's not going through the so-called "dead arm" phase.
"In a number of occasions, he's been close to wiping out the inning, and just hasn't finished it," Rothschild said of Marmol, who led the National League last year in inherited runners stranded. "It's just a few little things that are adding up to make a major difference."
The change in Marmol's stance has gotten him back to throwing strikes, so that's not the problem. Rothschild has seen pitchers go through this.
"It's not that unusual, but for a guy with his stuff and has had his success, you just wait for the worm to turn because it will," Rothschild said.
The toughest part may be convincing Marmol that this won't last long.
"He's had a lot of success since the first year he was in the big leagues," Rothschild said. "As a player, you never expect this to happen. The perspective is the biggest thing. This is a bump in the road, so let's get back on track. It's focus on the small things, the pitch at hand, and that's it. You make that pitch, and go on to the next pitch, and don't go any further than that."
The Cubs did tweak their bullpen. Jose Ascanio was optioned to Triple-A Iowa to make room on the 25-man roster for Carlos Zambrano, who was activated from the disabled list and started in the series opener against the St. Louis Cardinals on Friday.
Sean Gallagher, who started on Thursday, now is in the bullpen. Rothschild said he sees Gallagher as a starter, and has been encouraged by how he's pitched this year.
"I like the way he's progressed," Rothschild said. "For the time being, to help us get through the period, he'll go in the bullpen."