The San Francisco Giants acquired Carlos Beltran from the New York Mets in exchange for Zack Wheeler.
The Giants' offense is the worst in the National League by wRC+ (83) and Beltran was the best hitter available. The Giants' outfielders have combined for a 101 wRC+ on the season. Beltran's wRC+ this year is 152, so he's an obvious improvement.
I'm not sure what current outfielder is going to lose the most playing time. Beltran used to play CF but those days appear to be past him. All of his games in '11 have been in RF and most defensive metrics rate him as an average fielder there. That means he's unlikely to displace Torres and Rowand in CF. That leaves Schierholz, Ross, and Burrell. All are hitting similarly on the season:
PLAYER: OBP, SLG, wRC+
Ross: .342, .404, 108
Schierholz: .326, .438, 109
Burrell: .342, .419, 113
Schierholz has a reputation as a good defensive player. His career UZR/150 is 12.
Burrell has a reputation as a poor defensive player. His career UZR/150 is -6.6.
Ross has a reputation as an average defensive player. His career UZR/150 is -1.1
Nice when it works out like that.
Those number don't quite hold up for this season, as Schierholz has a -2 UZR, Ross has a -17 UZR and Burrell has a -13 UZR. But, larger samples are more reliable.
What's likely is that Beltran will continue in RF while Schierholz and Ross/Burrell platoon in LF. Using that assumption Beltran will provide the Giants with about 2.2 WAR (assuming he continues performing at his current pace). The other 3 Giants OFers were on pace to provide an additional 1.2 WAR over the rest of the season.
Using that, the trade looks to give the Giants 1 additional win over the season. Since Beltran is a free agent after the season that is his total value to the team.
The Giants have a 3.5 game lead on the Diamondbacks and coolstandings gives them a 68% chance of winning their division. Adding another win only increases these odds.
But, this trade wasn't really made for this regular season. While the Giants' offense has been the worst in the NL, their pitching has been the best (behind the Philadelphia Phillies). This trade was made with the playoffs in mind. Instead of hoping for Ssory Doc style heroics, Giants GM Brian Sabean, is trying to force the action by adding to the Giants lineup.
What's a run at back-to-back World Championships worth?
Wheeler was regarded as the Giants' #1 or #2 prospect with Brandon Belt being the other. Wheeler was the 6th pick in the 2009 draft. His minor league career has been brief but intriguing. In 146.6 innings he has a 3.99 ERA (3.99 in 2010 and also 2011) 5.2 BB/9 (13%) and 10.2 K/9 (26%). His stuff is loved by the scouts but the control hasn't been where you'd want it to be from a top prospect.
All pitching prospects are dicey propositions. Especially those who are 20 years old, pitching in A-ball and having control issues.
Still, the Mets did good to wrest him away from the Giants. Beltran had little value to the Mets the rest of the way. The Giants felt they had to take a chance to put themselves in position to win another WS. With Lincecum, Cain, and Bumgarner they could afford to move another young pitcher. The Mets are taking a chance with a high-upside pitcher. They were able to increase his value as he was the best player available and could pit teams against each other in the bidding.
Wheeler was a steep price to pay for 2 months of Beltran but it was an aggressive move. The Mets maximized their return. No guarantees that this deal works out for either team, but neither team can really be faulted for making it.