12 Pitchers You Wouldn't Trust to Come Up Big in a Pennant Race

Buckle up—MLB contenders are preparing to sprint the final leg of the American and National League pennant races.

None of them can afford to be tripped up by a trusted pitcher who slumps down the stretch (and proverbially ties the club's shoes together).

I'm providing a generous service for managers of the 12 winningest teams—identifying which of their reputable arms should not be used in high-leverage situations from here on out.

Deriding each staff's mop-up man would be too easy, not to mention insignificant. Those players are never given opportunities in close contests, anyway.

Rather, I'm calling out the Jekyll-and-Hyde starters, shaky setup men and wild closers who must be relieved of too much responsibility before the season is lost.

Ben Sheets (Atlanta Braves)

From 2004 to 2008, Ben Sheets was a legitimate MLB ace.

His results through five 2012 starts have been terrific (4-1, 1.41 ERA, 1.19 WHIP), though I fear that they're unsustainable.

Per FanGraphs, the right-hander's velocity is at an all-time low. He's also showing less faith in it and becoming increasingly insistent on feeding batters his show-me slider.

Sheets could thrive as an extreme fly-ball pitcher. Outfielders Michael Bourn and Jason Heyward are beastly defenders, and Turner Field is a spacious venue.

However, the 34-year-old doesn't operate like that anymore.

Luis Ayala (Baltimore Orioles)

Conventional stats don't accurately reflect Luis Ayala's 2012 performance.

His 2.60 ERA and 1.27 WHIP are respectable, as is his 3.09 strikeout-to-walk ratio.

Of course, relievers need to be held responsible for stranding inherited baserunners too. Ayala isn't particularly adept at shutting down the opposition when entering mid-inning.

More than 56 percent of previously put-on players have come around to score against him.

Francisco Liriano (Chicago White Sox)

When Francisco Liriano controls his off-speed stuff, he can be practically unhittable.

But the Chicago White Sox shouldn't be too eager to keep him in the starting rotation down the stretch and into the postseason.

Liriano doesn't pitch efficiently, even when amassing swing-and-misses. He records a lot of strikeouts, just not many of the three-pitch variety, and that inability to put batters away causes his pitch count to rise.

Chicago's bullpen has logged fewer innings than any other in the American League. Liriano's brief outings will rob the relief corps of that distinction, which could compromise its effectiveness.

Homer Bailey (Cincinnati Reds)

Homer Bailey dreads pitching at home.

Unfortunately, the Cincinnati Reds will play the majority of their remaining games at Great American Ballpark. At this rate, they'll also host most playoff contests.

As you can infer from his first name, the 26-year-old is susceptible to round-trippers. He has surrendered 15 through 12 outings in Cincinnati this season,and 46 in 55 career tries at that hitters' heaven.

Be very careful with him, Dusty Baker.

Jose Valverde (Detroit Tigers)

Watch Jose Valverde for about two minutes and you'll understand why I don't believe him to be a competent closer.

He's lacking zip on his fastball in 2012, yet attacking opposing batters like he always has. Not surprisingly, his whiff rate has dropped, and his earned run average has risen.

Simply by stepping on the mound, Valverde takes his teammates on an adventure. That held true last fall, as he let runners get into scoring position in five of six appearances last postseason.

Chris Capuano (Los Angeles Dodgers)

Chris Capuano (10-8, 3.29 ERA, 1.23 WHIP) is in the midst a fine campaign, but his endurance issues are cause for concern.

His pitching deteriorates after 75 pitches. Beyond that threshold, his OPS against spikes up to .804.

Moreover, the quality of Capuano's work suffers on the standard four days rest.

We could see that come back to bite the Los Angeles Dodgers in the near future. They have only one off day remaining in August.

Joba Chamberlain (New York Yankees)

Since returning from Tommy John surgery on August 1, Joba Chamberlain has been throwing gas.

That doesn't mean he's ready for close-and-late situations.

The hefty right-hander is committed to integrating a changeup into his game plan. So far, though, it has been easy for batters to align it with the sweet spot.

Chamberlain is locating poorly and getting crushed for it.

James McDonald (Pittsburgh Pirates)

This selection was pretty obvious.

James McDonald has allowed more runs than anybody since the 2012 All-Star break. Over those six starts, he hasn't survived into the seventh inning.

The Pittsburgh Pirates possess a surplus of viable starters, and McDonald will be the odd man out of their crowded rotation if this slump persists.

His nasty curveball is useless when his heater yields extra-base hits.

Tim Lincecum (San Francisco Giants)

Three years ago, Tim Lincecum was the National League's top player, somebody whose pitching couldn't be criticized.

A lot has changed.

The Freak has clearly made adjustments since spending the season's first half as a punching bag.

Still, his tendencies to struggle at the start and end of games is frustrating. He'll occasionally implode in the first frame or cruise through five and suddenly hit a wall.

Marc Rzepczynski (St. Louis Cardinals)

Marc Rzepczynski hamstrings St. Louis Cardinals manager Mike Matheny because he's so vulnerable versus right-handed batters.

This southpaw recorded huge, late-season outs for the Cards in 2011 on their run to the World Series. Back then, his platoon splits weren't quite so dramatic.

He has regressed, however, into a run-of-the-mill LOOGY. That became clear when Scott Van Slyke took him deep on May 20.

Roy Oswalt (Texas Rangers)

Roy Oswalt hasn't been a reliever since May 2001, his first month in the big leagues.

He hated it then, just as he does now.

The acquisition of Ryan Dempster by the Texas Rangers led to his demotion. Oswalt's ego isn't allowing him to acclimate to the new role.

Jon Morosi of Fox Sports delves deeper into his attitude problem.

John Lannan (Washington Nationals)

John Lannan won't rejoin the Washington Nationals rotation today, tomorrow or next week, but rest assured, his call-up from Triple-A is inevitable.

Via Twitter, Jeff Passan of Yahoo! Sports reported that phenom Stephen Strasburg will be shut down for the summer before reaching 180 innings. That information comes directly from GM Mike Rizzo.

Strasburg is on pace to exhaust those bullets in September. At that point, his spot will be given to the junk-throwing Lannan, a pitch-to-contact 27-year-old who tires out his fielders with his inability to induce a swinging strike.

Hopefully the Nats will have clinched a playoff berth by then, because nobody trusts this guy.

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