Multiple third basemen were involved in trades in July last year, as the Diamondbacks added Chris Johnson, the Rays picked up Ryan Roberts, and the Yankees traded for Casey McGehee.  The Astros acquired current starter Matt Dominguez from the Marlins, who themselves added Zack Cox from the Cardinals later that month.  The Cubs acquired a third base prospect as well, getting Christian Villanueva from the Rangers.

This year, contenders such as the Yankees, Dodgers, Indians, and Red Sox could be in the market for help at the hot corner.  Here's a look at the potentially available players.

Starters

Chase Headley (Padres), Aramis Ramirez (Brewers), Michael Young (Phillies), Alberto Callaspo (Angels)

It's been made pretty clear by this point that the Padres don't intend to trade Headley, and would like to talk about an extension during or after the season.  Still, it's hard to ignore the Padres dropping nine straight and Headley's solid play since the end of his abysmal June.  GM Josh Byrnes would surely at least listen to offers this month, wouldn't he?  

Ramirez, also one of last year's best offensive third basemen, does seem eminently available.  There are three problems with that.  One, he's 35 and may be slipping defensively, perhaps to the point where an AL team wouldn't expect or want him at the hot corner for all of next year.  Two, he's under contract for 2014.  That's not necessarily a problem until you see that he'll earn a $16MM salary plus a $4MM buyout on a mutual option, essentially making him a $20MM player next year (not counting a discount for deferred money).  Ramirez has shown repeatedly that he can provide $20MM worth of value.  However, bringing us to our third issue, he's slugging just .414 this year.  That may be nothing more than a month-long slump, but the timing isn't great for the Brewers if they want to get out from the contract, get back solid young players, or both.

Young, in his first crack at the National League, has fared mildly better than in 2012.  At this point the 36-year-old is a complementary offensive player with a poor defensive reputation and a good clubhouse reputation; a contender may pick him up mostly for that reason.  Callaspo is a similar player in some ways, but he's signed through next year.

Backups

Cody Ransom (Cubs), Luis Valbuena (Cubs), Kevin Frandsen (Phillies), Placido Polanco (Marlins), Jamey Carroll (Twins)

The Cubs' third base platoon has been highly effective, as their .766 OPS at the position ranks fifth in the NL.  Ransom can be under control next year as an arbitration eligible player, while Valbuena can be controlled through 2016.  Add in strong part-time work from Frandsen, who is under control through 2015, and the trade market features backup options who have outplayed many regulars in limited samples.

Other Possibilities

Lonnie Chisenhall, Will Middlebrooks, and Mike Moustakas were once among the best third base prospects in baseball, but development has stalled on all of them.  The Indians' Chisenhall, called back up on June 18th, has been playing well of late and seems the least likely to be included in a deal.  In general, I don't picture the Indians, Red Sox, or Royals giving up on these players this summer.

Biogenesis Effects

Alex Rodriguez is tied to Biogenesis, and could theoretically be slapped with a suspension shortly after making his season debut.  Regardless of Biogenesis, though, A-Rod's effectiveness and ability to stay on the field following January hip surgery is a huge question mark.  The Yankees would be well-served to explore reinforcements at third base with Kevin Youkilis on the 60-day DL.

You can also check out our trade market posts for catchers, first basemen, second basemen, and shortstops.

Last July, shortstops were on the move.  A legitimate shortstop prospect was traded when Jean Segura went to the Brewers from the Angels in the Zack Greinke deal, and now Segura is an NL All-Star.  The Dodgers acquired a player who had been one of the game's best shortstops, getting Hanley Ramirez from the Marlins.  Eduardo Escobar went from the White Sox to the Twins as part of the Francisco Liriano trade.  The Indians picked up Brent Lillibridge from the Red Sox; he played some short for Cleveland last year.  The Braves acquired Paul Janish from the Reds, while current Mets starter Omar Quintanilla was dealt to the Orioles.

This year, contenders such as the Pirates, Yankees, Cardinals, and Reds could seek a shortstop in some capacity, while any number of non-contenders may seek to add to their prospect stash at the position.

Starters

Jimmy Rollins (Phillies), Alexei Ramirez (White Sox)

Much has been written about whether the Phillies, currently 7.5 games back, will be trade deadline sellers.  Even if they do go that route, the 34-year-old Rollins has full no-trade protection and is under contract through at least 2014.  The Phillies still have Freddy Galvis and did acquire backup John McDonald recently, so they have options if they find a trade partner and Rollins approves.  Ultimately I don't think the Phillies could get a lot back for Rollins, so it makes more sense to hang onto the city's longest-tenured athlete.

Ramirez is worth a mention mostly because the White Sox are out of contention.  The 31-year-old is an acceptable option at short, hitting .277/.305/.342 with great durability and a reasonable contract that runs through at least 2015.  The extended control could put some non-contenders in play for Ramirez, if he's even available.  I was surprised to see Ramirez's age; this is not a player in his prime.  I think the return would have to be interesting for the Sox to pull the trigger.  Ramirez is not a player they need to unload, and naming Gordon Beckham the full-time shortstop requires a leap of faith.

Backups

Omar Quintanilla (Mets), Adam Rosales (Athletics), Ronny Cedeno (Astros), Brendan Ryan (Mariners), Ruben Tejada (Mets), John McDonald (Phillies), Jamey Carroll (Twins)

It's always good to add veteran insurance; a glove man like Ryan could help a contender.

Other Possibilities

With 20-year-old shortstop prospect Javier Baez getting a promotion to the Cubs' Double-A affiliate recently, is there even a sliver of a chance the team would consider trading Starlin Castro?  Though Castro was not brought in by the Epstein/Hoyer administration, and he's not the type of hitter they generally prefer, a midseason trade seems highly unlikely.  Castro's terrible season would mean selling very low, high-walk shortstops barely exist anyway, and the front office made a major contractual commitment to him just last August.

With no regular spot for him, the Rangers have turned one of the game's best prospects, Jurickson Profar, into a temporary utility man.  If they are to trade him, they'd surely require one of the game's best players in return, such as the Marlins' Giancarlo Stanton.  There's no indication the Rangers are open to putting Profar in a deal, though.

Eduardo Nunez missed significant time with an oblique injury, but he's now the Yankees' starting shortstop until Derek Jeter's season debut.  The team seems unlikely to move Nunez given the uncertainty with Jeter's health.

Biogenesis Effects

A couple of All-Star shortstops have been linked to Biogenesis in the Padres' Everth Cabrera and the Tigers' Jhonny Peralta.  Having dropped nine in a row, the Padres' status as a contender is slipping, so they may not need to act if Cabrera is suspended.  The Tigers' alternatives include Ramon Santiago, Argenis Diaz, and Danny Worth, so I imagine they'd have to make an acquisition if Peralta is suspended prior to the August 31st waiver trade deadline.

You can also check out our trade market posts for catchers, first basemen, and second basemen.