The trade between the Cardinals and A's involving Matt Holliday looks like a win for both teams -- Oakland gets a strong troika of prospects that's better than what it gave to Colorado for Holliday seven months ago, while St. Louis gets a much-needed offensive boost that should greatly improve its chances of making the playoffs.
Holliday started his tenure with Oakland horribly, bottoming out after an 0-for-7 performance in an extra-inning loss to Seattle on May 3 and an 0-for-4 performance the next day against the Angels. Since then, in exactly 300 plate appearances, he has hit .310/.413/.492, more in line with his skill set and history. He's a great athlete and a strong and disciplined hitter who can adjust to off-speed stuff and who murders mediocre pitching. He offers above-average defense in left field, although he looks bad doing it (advanced defensive metrics consistently rate him as above average). The knock on Holliday at the plate has always been that he can't handle heat -- throw him hard stuff, especially in on his hands or up in the zone, and he can't catch up. He'll now move back to the National League, which has less velocity overall and more starters who survive with fringe-average or below-average fastballs. So there's good reason to believe he'll improve his performance by more than the typical player who leaves both the American League and Oakland's cavernous park.
The Cardinals have an average offense right now, but one that's heavily concentrated in the bat of Albert Pujols, giving them plenty of room for improvement in the other seven spots in the lineup. Both Rick Ankiel and the excised Chris Duncan were below replacement level this year, with Duncan compounding the problem with his standard butchery in the field. So Holliday is probably worth three or nearly three extra wins to the Cardinals for the rest of the year, and that's assuming that he doesn't recover more of his lost offense by leaving the American League and a bad ballpark in Oakland. Three wins is enormous for a team that is currently in a four-team jumble separated by two games in the loss column, and on paper at least makes the Cardinals the most likely team in the division to finish on top.