Buyers or sellers?
The Marlins are 6.5 games behind the division leading Phillies with a 51-48 record. That is a bit of a gap to make up but they are also only 3.5 games behind the Rockies in the Wildcard race. Marlins' executives have said that they will be buyers, but given their standing in the playoff races that decision could really come down to how the play in the next week. Their performance in that time frame could determine whether they are selling off veterans or adding pieces in an attempt to make the playoffs. The most likely scenario though is probably that the Marlins stand pat and wait to see how the season plays out.
Other than Hanley Ramirez there isn't another standout position player on the Marlins right now. That said, the most logical spots for an upgrade right now are at either corner outfield spot or at third base. Jeremy Hermida's atrocious defense takes away all of his value offensively and Chris Coghlan hasn't hit enough to help the team. The Marlins have tried other options in the outfield such as Cameron Maybin and Alejandro De Aza but they aren't helping either. At third the platoon of Wes Helms and Emilio Bonafacio isn't working as neither of them have done anything offensively. A big bat at any of these three positions would go a long way in helping the offense.
On the mound Josh Johnson and a recovered Ricky Nolasco form a fiersome duo at the top of the rotation. The problem is that beyond them there is a huge dropoff. Chris Volstad has been solid but Andrew Miller had to be demoted to Triple-A and there hasn't been a set fifth starter. An established starting pitcher would give the rotation a boost but the Marlins aren't likely to go after a rental player such as Jarrod Washburn. Unless they shoot for an ace they might not be able to find a replacement that is a definite upgrade.
The Marlins also haven't gotten much out of their bullpen. Closer Matt Lindstrom is currently on the DL but was too wild to be effective even when he was healthy. Kiko Calero has been the team's best reliever and Burke Badenhop and Leo Nunex have also done solid work. This might be the easiest area for the Marlins to trade for an upgrade wthout paying too much in either prospects or salary.
For the long term the Marlins shouldn't have too many positional needs if most of the prospects develop as planned. The infield should have John Baker, Hanley Ramirez, Matt Dominguez, and either Logan Morrison or Gaby Sanchez at first base. That means the only open spot is at second base where Dan Uggla will likely move on in the next few years. The outfield should be filled by some combination of Cameron Maybin, Chris Coghlan, Cody Ross, Jeremy Hermida, and Michael Stanton.
So that means that the Marlins need to focus on improving their pitching. They have some young arms for the rotation but given the team's extremely low payroll there's no telling how long they will be able to keep guys like Johnson and Nolasco. That means the farm system needs to keep churning out pitchers, something it lacks right now. The bullpen also needs work as there aren't any shutdown relievers in the organization. Signing late inning relievers is expensive on the open market so the Marlins will have to use some pitchers from inside the organization to fill out the 'pen.
Big leaguers on the market?
Unless the Marlins front office decides to be sellers there shouldn't be many major leaguers on the market. If they are, Dan Uggla and Jeremy Hermida could both find their way out of town to save the team money for next season. But if the Marlins are buyers then those two are probably staying. The most likely candidates on the major league roster would be guys who are bouncing back and forth from the minor leagues like Gaby Sanchez and Andrew Miller. Either of them could be traded for upgrades at key positions if the Marlins decide this is their year to make a run at the playoffs.
Minor league strength
The Marlins have a strong farm system with a number of possible impact players within arm's reach of the big leagues. However, most of these players are positon players, not pitchers. Their top pitching prospects, Ryan Tucker and Sean West, haven't lived up to expectations so far this year (Tucker because of injuries and West because of general ineffectiveness).
The impact hitters include Cameron Maybin, Logan Morrison, Michael Stanton, and Matt Dominguez. Maybin was one of the key players in the Miguel Cabrera trade with the Tigers. He's a very toolsy center fielder who is still developing his hitting skills at Triple-A but should be a full-time starter by next year. Morrison is a slugging first baseman with outstanding plate discipline. He missed two months of the season but has walked 39 times so far this year and has only 25 strikeouts. Stanton is an outfielder with light tower power but a huge strikeout problem. He hit 39 homeruns last year in Single-A at age 18 and has 21 homeruns between High-A and Double-A this year in only 320 at bats. The problem is he's also struck out 95 times, so he's going to have a tough time hitting for a high avetage in the majors. Finally, Matt Dominguez is a stellar defensive third baseman who's also holding his own offensively in High-A at only 19 years of age. The Marlin's offensive future looks very bright.
Take on short-term money to win?
While it looks like the Marlins might try to add a player or two at the deadline, they don't want to add much salary. If they trade for a player with a large contract they would probably need the other team to pay for most of it.
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