By Cliff Corcoran

With the All-Star Game behind us and the non-waiver Trade Deadline two weeks from Monday, the swapping season is upon us, as evidenced by the Cubs' acquisition of Jose Quintana. So, here are the 10 players believed to be on the trading block who were the most valuable in the first half according to Baseball-Reference's wins above replacement player.

10. Jay Bruce, RF, Mets (2.0 bWAR)

.266/.334/.538, 23 HR, 59 RBIs

The Mets added Bruce at last year's Deadline, then picked up his $13 million option, and they're likely to trade him away at this year's Deadline given the 30-year-old's impending free agency. Bruce has been roughly as productive for New York this year as he was for Cincinnati last year, when the Mets sent the Reds second-base prospect Dilson Herrera and 2015 third-round pick Max Wotell for him. However, Bruce's poor post-trade performance last year (.219/.294/.391) and status as a two-month rental will diminish his market value significantly. Further complicating things, he can block trades to the Yankees, Rays, D-backs, Twins, Blue Jays, A's and Marlins. He'd be a good fit in Kansas City if the Royals decide to go for it, but his left-handed power and ability to play first base could make him attractive to the cross-town Yanks if Bruce would be willing to approve that deal.

9. Jed Lowrie, 2B, A's (2.3 bWAR)

.279/.346/.458, 9 HR, 32 RBIs

Pending free agent Yonder Alonso was the A's lone All-Star and has inarguably been better at the plate than Lowrie this season. However, when you factor in defense, Lowrie was the A's best player in the fist half, at least according to bWAR, which punishes Alonso for his fielding with a 1.3 bWAR. Lowrie has played second base exclusively this season, but has extensive experience at third and short and, with a $6 million club option for next year, could be a nice utility addition, the sort of player who can keep a team from dropping down to replacement level at one of several positions. He'd be exactly the kind of low-cost pickup that could help keep the Brewers competitive in the second half, or could serve as a third-base stop-gap for the Yankees or Red Sox, then fall back into a utility role once those teams' elite infield prospects arrive next year.

8. Alex Avila, C, Tigers (2.3 bWAR)

.299/.423/.535, 11 HR, 29 RBIs

Avila is a 30-year-old on an inexpensive one-year contract (he's making a mere $2 million this season) having a wild small-sample surge at the plate. He's also a catcher, which is a rare commodity to find on the midseason market. He's not a very good catcher, mind you -- he's a poor framer with a worrisome history of concussions -- but he has usurped James McCann as the starter in Detroit based on his huge first-half performance. Avila should draw plenty of interest, particularly from the Nationals, whose catchers have hit .216/.272/.340 this season, the Indians (.208/.299/.328), the Rockies (.235/.309/.313), the Red Sox (.256/.298/.370) and the D-backs (.206/.268/.431).

Speaking of the Tigers, their right fielder, J.D. Martinez, another impending free agent, did not make this list because he missed a month due to injury and has a mere 1.3 bWAR on the season, but he has hit .299/.381/.610 since his return and may be the best bat on the market this month.

7. Jarrod Dyson, OF, Mariners (2.4 bWAR)

.258/.340/.391, 48 R, 20 SB (80 percent)

A league-average hitter with elite footspeed (he's the pink dot here) who offers an outstanding glove at any outfield position is a very valuable player, particularly as a fourth outfielder on a contender. Just ask the Royals, who would surely be interested in getting Dyson back if they decide to buy and the Mariners decide to sell. Dyson would be a valuable addition for just about any team, but he might fit best in Washington or Tampa Bay, both of which have lost multiple outfielders to injury. Dyson will be a free agent in the fall, so you can be sure he'll be on the block if the M's falter early in the second half. Given that they'll face the Astros, Yankees and Red Sox in succession starting Monday, that's a distinct possibility.

6. Avisail Garcia, RF, White Sox (2.6 bWAR)

.310/.353/.497, 11 HR, 51 RBIs

Breakout star Garcia has two arbitration years remaining, so the White Sox are under no pressure to trade him. However, Chicago has clearly set its sights beyond 2019 given that they dealt Chris Sale and Adam Eaton over the winter and have now dealt Quintana, all of whom are under team control for as long or longer than Garcia. Meanwhile, Garcia's value may never be higher. He looked like a busted prospect coming into his age-26 season, and after a monster April, his production slipped in both May and June. Given that, there may be some urgency here, after all. The Boston Globe's Nick Cafardo reported last month that the Cardinals could have some interest in Garcia. Those two years of team control would certainly be a factor there, as St. Louis is below .500 and has just a 21.9 percent chance of making the playoffs this year per Baseball Prospectus's Playoff Odds Report.

5. Lorenzo Cain, CF, Royals (2.7 bWAR)

.274/.346/.435, 11 HR, 30 RBIs, 15 SB (100 percent)

There is a very large "if" attached to four of the top five men on this list. For Cain, that "if" is "if the Royals decide to sell." That's far from a given. Entering the second half, they are just three games out of first place in the American League Central and 1 1/2 games out of the second Wild Card spot in the AL. However, they are just one game over .500, they have a third-order winning percentage of .463, and Baseball Prospectus gives them a mere 17.2 percent chance of reaching the playoffs. What makes that decision especially complicated is the quality of players the Royals have to offer this month and the risk involved in not cashing them in before they hit free agency this fall.

Cain is the best of the Royals' pending free agents, but he's a poor candidate for an extension given that he's already 31 and has only surpassed 120 games played in a season twice due to a checkered injury history. If Kansas City goes for it and misses, Cain would have to land a $50 million deal in the offseason to net Kansas City compensation for his departure. That seems likely but not a given per his age and fragility. Meanwhile, just imagine how much better he would make the Nationals, the Cubs, the Dodgers, or the Brewers (though the last may hesitate to spend big on a rental). The Royals have a relatively soft schedule coming out of the break, but if they stumble against the likes of the Rangers, Tigers and White Sox, they had better shift into sell mode quickly.

4. Giancarlo Stanton, RF, Marlins (2.7 bWAR)

.277/.360/.572, 26 HR, 58 RBIs

Is dealing the biggest star in Miami far-fetched? On Sunday, Jon Heyman quoted Marlins president of baseball operations Michael Hill as saying, "we aren't talking about," trading young, team-controlled stars Marcell Ozuna, Christian Yelich, Justin Bour and J.T. Realmuto. Hill didn't put Stanton in that group, however, only saying, "we haven't put his name out there," meaning on the market. Earlier in the month, video star Ken Rosenthal suggested that, despite Stanton's massive contract (he's owed $295 million for the next 10 seasons), full no-trade clause and 2020 opt-out, which further complicates any trade evaluation, a Stanton trade isn't impossible. Indeed, as great a star as Stanton is, the new ownership -- whoever that may be -- could prefer to be free of his record-setting contract, particularly given Stanton's injury history and the fact that the contract will take him through his age-37 season if he doesn't opt out. Meanwhile, for teams contemplating making a run at Bryce Harper after next season, Stanton would actually represent a cheaper alternative, albeit one with a significantly lower potential impact. It seems extremely unlikely that a deal will get done, but it does appear that Stanton is at least somewhat available.

3. Zack Cozart, SS, Reds (3.0 bWAR)

.316/.394/.547, 9 HR, 34 RBIs

The Reds have made noise about extending Cozart, but giving a big contract to a 31-year-old shortstop who has already been twice as valuable at the plate this season as in any other year of his career would appear to be a massive "buy high" blunder. More likely, the Reds will do the right thing and finally trade the veteran after falling just short of a deal at last year's Deadline. If the Royals do decide to go for it, they should go after Cozart. The Brewers and D-backs should also have interest.

2. Ervin Santana, RHP, Twins (3.4 bWAR)

10-6, 2.99 ERA (150 ERA+), 1.08 WHIP, 6.8 K/9, 2.28 K/BB

Santana is another "if they sell" player. Entering the second half, the Twins are a half-game up on the Royals in the standings, but have a mere .424 third-order winning percentage and an 18.1 percent chance of reaching the postseason. Santana, meanwhile, is a 34-year-old league-average innings eater sporting an impressive season line, but with poor peripherals and a 4.20 ERA over his past dozen starts dating back to May 7.

Santana comes with up to two more years of team control, via a guaranteed $13 million salary for 2018 and a club option for 2019 that could vest if he stays healthy and throws 400 innings between this season and next. However, he would be owed $27.5 million for those two seasons, which will be his age-35 and -36 campaigns. There are many good reasons there to try to sell high on Santana and take advantage of a contender desperate for rotation help. The Astros might best fit that description, though the Twins may have to eat some of Santana's salary to get a quality return from Houston.

1. Jason Vargas, LHP, Royals (4.0 bWAR)

12-3, 2.62 ERA (174 ERA+), 1.15 WHIP, 6.6 K/9, 3.12 K/BB

Same caveat applies here that it did to Cain: If the Royals decide to sell, Vargas could be one of the players on the block (but, again, that is far from certain, especially if K.C. starts off the second half well). A 34-year-old veteran with a below-average career ERA+, Vargas is having a career year in his walk year, but without meaningful improvement in his peripherals. Currently in the final season of a four-year, $32 million deal, he seems like a long shot to land the $50 million contract that would net the Royals' free agent compensation come the fall. However, he is a more attractive option than Santana for a contender looking for rotation help given the lack of salary commitment and Vargas' more consistent performance this season. That said, it would be easier for the Royals to consider Vargas a nice surprise for which they need not be compensated than it would be for them to let Cain (or Mike Moustakas, or Eric Hosmer, both of whom should easily surpass $50 million as free agents) go without compensation. Exactly what the Royals will do remains to biggest question of this year's Deadline.

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Cliff Corcoran is a Sports on Earth contributor and a regular guest analyst on MLB Network. An editor or contributor to 13 books about baseball, including seven Baseball Prospectus annuals, he spent the last 10 seasons covering baseball for SI.com and has also written for USA Today and SB Nation, among others.