We've seen a flurry of activity a week removed from the trade deadline. The Tigers picked up Anibal Sanchez and Omar Infante. The Yankees added Ichiro Suzuki. The Dodgers nabbed Hanley Ramirez. The Astros made three deals in four days. We're sure to see more in the days ahead, as teams still in divisional and Wild Card races look to snag that final piece of the puzzle.
It's important to keep some perspective on the impact of these deals. MLB isn't the NBA or NFL, where one player can have a disproportionate impact on the outcome of a game or a season. The Colts lost their quarterback and went from a Super Bowl contender to the first pick in the draft. The Cavaliers lost a single free agent and slipped from title contender to afterthought. In baseball, you can't get your best player extra at-bats or ensure that the ball will be hit to your best fielder with the game on the line. You can only use your best pitchers so often, and even the one part of the game where teams can map usage to situations -- relief pitching -- finds that player impact is limited by the number of innings relievers throw.
When sabermetricians looked to evaluate how much value a single player could have, they found it was generally less than expected. In modern baseball, the best players in a given league tend to be worth about eight to nine wins a year, with some exceptions, and about 18 players a year -- less than one per team -- are worth six wins a year. Here's the breakdown for 2001-2011, using Baseball-Reference's Wins Above Replacement metric:
These numbers are important because they set a reasonable upper limit on how much you can improve your team with a single midseason trade. A six-win player projects to be worth two wins over the final two months of the season, so if you're adding a star and using him to cover for replacement-level performance, you can expect to be two wins better -- and that's a pretty extreme scenario. It's actually worse than it looks here, because players having better than six-win seasons rarely are traded during their big year. The only player among the 88 7.0-win-and-up seasons to play for more than one team was Mark Teixeira, who went from the Braves to the Angels at the deadline in 2008.
Now, players aren't stat-generating robots, so what we're dealing with here is projection and expectation. The natural variance of player performance means that sometimes you'll make a trade that is supposed to make you two wins better -- like the Dodgers with Ramirez -- and the player you acquire has a big two months and you get more than you expected. In 1998, the Astros acquired Randy Johnson to anchor their starting rotation, and got a ridiculous 11 starts of 1.28 ERA performance. It can go the other way, too. In 2009, the Yankees traded for Lance Berkman to bolster their lineup, only to get one homer in 123 plate appearances as Berkman couldn't adjust to the DH role.
The Tigers and the Dodgers have done well to make themselves two wins better in-season. What other players are out there who could have the same impact on a new team, should they be traded?