OAKLAND -- While his teammates have put together an encouraging offensive stretch, Cliff Pennington is in the midst of a frustrating one.

The A's shortstop, recently relegated to a platoon role with Brandon Hicks, entered Thursday's contest against the Yankees with four hits in his last 45 at-bats, spanning 16 games. He has none since the start of the second half, and his hitless performance Wednesday dropped his season average below the Mendoza Line to .199.

Pennington's .546 OPS is worst among all qualifying Major League shortstops, and his slugging percentage (.285) and on-base percentage are second-lowest in the American League.

"If we knew the exact recipe, certainly we would've addressed it," manager Bob Melvin said. "I think he's just grinding on himself pretty hard. He's used to hitting a lot higher, he's used to contributing a lot more on the offensive end. It's just kind of snowballing on him, and he's finding it tough to get out of it right now."

The switch-hitting Pennington has always been one of the club's streakier players, but his struggles have been season-long this time around, and they could ultimately influence the A's front office to reach out for middle-infield help -- Toronto's Yunel Escobar could be of interest -- should the club still be in contention just before the Trade Deadline.

Pennington, 27, is arbitration-eligible at season's end, so the A's aren't attached to him financially. They've always valued his defensive skills, but his offensive numbers will have to improve if he wants to regain a full-time role.

"You'd like to think that a good couple games, he'll be on a roll," Melvin said. "He's continually working toward that. He's as hard of a working guy as we have here right now, he just hasn't had the consistency or the confidence that normally he would have over the course of a season. It's just been a grind for him."

Dominant lefties highlight A's deep bullpen

OAKLAND -- Potential playoff teams scouring the open market for relief help in the coming weeks have to be envious of the pitching-rich A's.

Oakland's bullpen has quietly proved to be the best in the American League, compiling a league-leading 2.73 ERA and Major League-best .203 opponents' average and .319 slugging percentage. In 12 games in July, the relief arms have allowed four runs in 37 2/3 innings.

Perhaps they can be deemed the unsung heroes of Oakland's recent surge? Manager Bob Melvin seems to think so, and he doesn't take his bullpen talent -- or the fact he has three excellent lefties in Jerry Blevins, Jordan Norberto and Sean Doolittle -- for granted.

"We're very fortunate to have the type of left-handers that we do," Melvin said. "Blev might be the one down there that's more of a left-handed specialist, where we feel like Norberto and certainly Doolittle at this point get right-handers out just as well. We're lucky to have this many quality left-handers, not only here, but in our system."

Down under, the A's have southpaw Pedro Figueroa posting similar numbers for Triple-A Sacramento, where he has a 2.51 ERA with 29 strikeouts in 28 2/3 innings. The southpaw has had three stints with the A's this year already and figures to be a big league mainstay by season's end.

Each of the A's bullpen arms figures to remain with the club through the Trade Deadline, unless Oakland receives an overwhelming offer for Grant Balfour, who is expected to garner a high level of interest.

Worth noting

• Melvin said right-hander Brandon McCarthy, fresh off a Wednesday bullpen session, reported no problems with his right shoulder Thursday, so he'll throw another Saturday.

• Through the A's "Walk-Off a Hero" program, Budweiser is donating $5,000 to the Folds of Honor Foundation for every A's walk-off win this season. Oakland already has nine, meaning $45,000 has already been donated for the foundation, which provides post-secondary educational scholarships for children and spouses of military service men and women killed or disabled while serving.