As we approach the July 31 trade deadline, MLB teams are reworking their rosters as some teams prepare for the playoff push and other teams prepare for 2009. This is a great time for fantasy-league owners because several top prospects will be given starting jobs as early auditions for next year, while new roles will be created for other top prospects. Below is a list of the latest call-ups and their roles for the last two months of the season:

Josh Fields, 3B, White Sox: With Joe Crede landing on the DL with back problems again, Fields has been recalled from Triple-A Charlotte and given the starting third base job. Crede will be a free agent after this season, so this could be more than an audition for Fields. Honestly, it's been a wasted season thus far for Fields as he showed so much promise last year only to be bypassed for a job this spring and sent back down to the minors. In 100 games with the White Sox last year, Fields hit .244 with 23 homers and 67 RBIs, but he also struck out 125 times.

When Crede came to camp healthy Fields was demoted to the minors. In 59 games at Charlotte, he hit only .248 with nine homers, 30 RBIs and five stolen bases. He's definitely a worthy pickup for the stretch run, but with the White Sox in a pennant race Fields will have to perform right away to have any shot at playing time throughout September.

Steven Pearce, OF, Pirates: Pearce was promoted from Triple-A Indianapolis this week after the Pirates sent Xavier Nady to the Yankees, and he will now start in right field. The 2005 eighth-round pick out of South Carolina was ranked as Pittsburgh's third best prospect by Baseball America, but his progress has been less than impressive this year. In '07, he jumped from Class A to the majors as he pounded 31 homers and drove in 119 runs with 16 stolen bases. During a September call-up, he hit .294 with six RBIs, but he had a rough spring and landed in Indianapolis to start '08. In 93 games there, he hit just .258 with 11 homers, 54 RBIs and eight stolen bases, but he's been handed the right field job now and will be given every chance to succeed. The Pirates are rebuilding for the future, and Pearce is a big part of that future. He's also a worthy pickup now as he has the tools to succeed over the next two months.

Andrew McCutchen, OF, Pirates: There were also reports that the Pirates were on the verge of promoting McCutchen to the majors this week. If that happens, he could start in centerfield, with Nate McLouth moving to left field. McCutchen is the Pirates' top prospect according to Baseball America and he's definitely one of the fastest players in baseball today, with the potential to steal 30-plus bases a year whenever he reaches the majors. He's spent all of this season at Triple-A Indianapolis and was hitting .279 with nine homers, 40 RBIs and 26 stolen bases through 101 games, while posting a solid .369 on-base percentage. If he does get the call, he will definitely be a worthy pickup for the stretch run as he can be an impact player when he gets on base. He will be fun to watch, trust me.

Chris Volstad, SP, Marlins: The Marlins' No. 2 prospect according to Baseball America was called up to the majors on July 6 and is another worthy prospect for the stretch run. The Marlins may have rushed him from Double-A to the majors, but he's looked better with each outing and could remain for the playoff push. The '05 first-round pick went 4-4 in 15 starts this year at Carolina and had only 56 strikeouts in 91 innings, but in three starts with Florida he has gone 2-1 with a 2.38 ERA and 15 K's in 22.2 innings. He's gone at least six innings in all three starts and had six K's in two of them. Even though he's 6-foot-8 and 225 pounds, Volstad isn't going to overpower hitters, but he has a solid fastball and a great changeup and will continue to be successful at this level as long as he throws strikes. Grab him if he's still out there.

Jeff Samardzija, RP, Cubs: The former Notre Dame All-American wide receiver reached the majors in just two seasons after being a fifth-round selection by the Cubs in '06. He certainly struggled his first two years in the minors, but he turned things around once he got to Triple-A Iowa this year, going 4-1 in six starts with a 3.13 ERA and 40 strikeouts in 37.1 innings. He replaced Kerry Wood when he went on the DL and will work out of the bullpen, but don't expect much production out of him this year. He's more of a long-term project than a helpful addition in '08, but give him credit for getting to this point after spurning the NFL.

Other call-ups of note include veteran pitchers Chris Carpenter of St. Louis and Mike Hampton of Atlanta. Carpenter has been sidelined for 16 months after undergoing Tommy John surgery, but is scheduled to start on Wednesday after making two minor-league starts. He's been solid in those starts, posting a 1.86 ERA with nine strikeouts in 9.2 innings. The Cardinals could be accused of rushing him, but if he's available in your league he seems to be a worthy pickup. Hampton made his first start in almost three years on Saturday and was very shaky, giving up six runs in 4-plus innings. He's more of a risk than Carpenter, so proceed with caution there.

Washington and Pittsburgh both have new closers after trading their current closers in the past week. The Nationals sent Jon Rauch to Arizona, where he's now the setup man for Brandon Lyon, and will hand the closing duties to Joel Hanrahan. The 26 year old has never closed a game in his pro career, but he does have 67 strikeouts in 60.1 innings this year and is a worthy pickup at this point in the season. It's quite possible that Hanrahan is available in most every fantasy league in the country as the second-year pro had been a non-factor before the Rauch trade. Interesting.

The same could be true in Pittsburgh where John Grabow will take over the closer's job for Damaso Marte, who was traded to the Yankees. Grabow at least is a six-year veteran who had two saves before this year, but he's been more of a setup guy this year with 41 K's in 50.2 innings. He should also be available in most leagues around the country and is at least worth a shot for the last two months of potential saves.

Masahide Kobayashi is the new closer in Cleveland, but don't be surprised if newcomer Jon Meloan gets a look in that role this September. He was acquired from the Dodgers in the Casey Blake trade this week and was a former closer prospect before the Dodgers tried to convert him into a starter this year. At Triple-A Las Vegas, Meloan was 5-10 with a 4.97 ERA and 98 strikeouts in 105 innings. He should be converted back to a reliever and given a shot at the closer's job soon.

In Oakland, if the A's decide to trade Huston Street, Joey Devine could take over the closer's job if he can get healthy soon. Devine has been sidelined for the last month with a strained elbow, but looked good this week in a throwing session. Keep him on your radar if anything happens to Street because he could be the latest new closer to arrive on the free agent wires.

It's hard to believe, but Francisco Liriano is still at Triple-A Rochester with the Twins battling for the AL Central Division title. He pitched again on Sunday and took a 9-2 record, 3.13 ERA and 104 Ks in 112 innings into that game. Fantasy-league owners have patiently awaited his return to the majors, but 19 starts in the minors is more than they bargained for when they drafted him in March.

The Tampa Bay Rays are also in a fight for a divisional title -- their first in franchise history -- and may reach into the minors for help, too. SP David Price continues to impress at Double-A Montgomery as he's 4-0 there in six starts and now is 8-0 this year in the minors with a combined 2.01 ERA and 68 strikeouts in 71.2 innings. Can he help the Rays and your fantasy team in September if he gets called up? Absolutely, so keep him on your radar these last two months.

Good luck the rest of the way and get ready for a few more top prospects to arrive once the trading deadline is finished. They will help MLB teams, and your fantasy teams, too.

Greg Ambrosius is the director of the National Fantasy Baseball Championship -- the industry's only multi-city high-stakes fantasy baseball event. Send questions to Greg at greg.ambrosius@fwpubs.com.

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