Williams explains lineup logic, says Fister's stuff will play at Coors (updated)

In his last six games, Bryce Harper has raised his average from .246 to .263 and hit a pair of home runs. Ever since taking a more upright approach at the plate, he's been raking.

So why is Harper on the bench tonight as the Nationals open a three-game series at Coors Field against the Rockies?

Manager Matt Williams told reporters in Denver that the reason is two-fold: He wants to give Harper the occasional day off, especially since he seems to be struggling lately against left-handed pitching, and he wants to improve the infield defense behind right-hander Doug Fister, a groundball pitcher making his first career start at Coors Field.

So Harper is on the bench to start tonight's game, with third baseman Ryan Zimmerman taking over in left field, Danny Espinosa playing second base and Anthony Rendon shifting from second to third base. Right now, that's the Nats' best defensive infield in terms of fielding, arm strength and accuracy.

"He's going to get days on occasion," Williams said of Harper. "He hasn't been seeing lefties as well as he wants to. So it's a question of giving Danny some at-bats right-handed, certainly, and allowing Zim to get some time in left, too. So I think that's just the basic rationale behind it."

With the Rockies throwing three straight left-handers at the Nationals during this series - Franklin Morales, tonight's starting pitcher, will be followed by southpaws Johan Flande on Tuesday and Jorge de la Rosa on Wednesday - it's possible Williams could give another left-handed hitter a day off. First baseman Adam LaRoche and center fielder Denard Span are possibilities for a blow.

If LaRoche sits, Zimmerman could get a start at first. If Span rests, Harper could shift to center.

"It's just a day. It's not like he's not going to play against lefties," Williams said of Harper.

Williams is cognizant that Harper is still playing his way back into shape after spending weeks on the disabled list following surgery to repair a torn thumb ligament. And the manager thinks lefties have been particularly tough on Harper of late, despite the outfielder's .359 average against left-handers in 22 games this season.

"It's just balls down out of the strike zone, (he's) not seeing those as well," Williams said. "We've got to give him some days, too. He's coming off a very serious injury."

It's clear that infield defense is a key whenever Fister pitches, and Williams is hoping that the right-hander can keep the ball on the ground and out of the thin Denver air that can torment pitchers.

"Doug's a groundball guy," Williams said. "Hopefully, tonight, Danny can use his skill at second base and we can move Anthony over to third. See if we can beat these guys ."

Espinosa has made only two starts in July and Williams wants to keep him sharp.

"He's been doing some defensive stuff, getting a pinch-hit (appearance) here and there," the manager said. "But he hasn't played a lot. We want to continue to try to continue pick our spots and get him some time out there."

Fister wasn't originally scheduled to start during this series, but when Gio Gonzalez missed a flight out of Miami because of mechanical issues, it forced the Nats to tinker with their rotation.

Williams doesn't think there's any magic bullet to pitching in Coors Field, and readily admits that part of the pre-series pitching meetings focused on the idea that runs will likely be scored there instead of tight pitchers' duels.

But Williams still thinks Fister's stuff will play in the Mile High City.

"It's the ability to change speeds that I think is effective here," Williams said. "Regardless of velocity or any of that, the ability to change speeds and get hitters off-balance will help you here. And that's Doug, that's what he does. Everybody talks about well, the sinker doesn't sink as much and the curve doesn't as much. It's not really a question of that for me, it's about a change in velocity. ... We want him to do what he does. He can't change the way he pitches because he's in this ballpark."

Update: Harper struck out swinging as a pinch-hitter in the seventh.