The New York Mets needed another impact bat to replace Carlos Delgado, whose 2008 second-half surge was a big part of why the Mets had a lead to blow in the NL East that fall. Jason Bay should be that guy with his plate discipline, power and 200-plus games of experience in the toughest division in the game. Citi Field is a pretty good fit for Bay, as it's a good park for right-handed power hitters (plus-10 percent versus a neutral NL park, according to this year's Bill James Handbook).
The question of whether this is a reasonable deal for the Mets or a massive overpay revolves around the question of just how far below average Bay's left-field defense is. Various advanced defensive metrics, including UZR, all show him as awful during the past three years, starting in his injury-wrecked 2007 season and continuing through his year-plus in Boston. Evaluating defense (quantitatively, that is) in Fenway is difficult because of the park's unique dimensions in left and center field, and it's possible that the metrics are all underrating Bay because of that factor. His range is fringe-average, and he reads the ball fine off the bat, but his first move isn't quick (maybe a remnant of his earlier knee injury), and his arm limits him to left field anyway.
I think there's a strong chance that Bay will outperform defensive expectations to the point where his salary no longer seems out of line with his performance because he'll do the things at the plate -- get on base and hit for power -- that pay the bills.
The move probably pushes Fernando Martinez back to Triple-A, a level where he's performed well, although the developmental goal for him is to stay healthy rather than show he can hit minor league pitching. Jeff Francoeur most likely will turn back into a pumpkin before the All-Star break, giving Martinez an opening to return to the majors if he's not on the disabled list.
The bigger problem for the Mets, however, is that Bay can't pitch, and to start the season, the team plans to run out exactly one starter who's likely to be playoff-caliber. Mike Pelfrey, for all his promise, took a step back in 2009 with an 84 ERA+ and is just an innings-eater until he misses more bats. John Maine is coming off a half-season ruined by shoulder weakness that could recur at any time. Oliver Perez might not make the Triple-A Syracuse rotation if it weren't for his contract.
The Mets need another starter if they want to contend in a pretty strong division -- the Phillies are the class of the NL, and both the Braves and Marlins are ahead of the Mets on paper -- and they're already over $120 million in commitments for 2010. Yes, the Mets will sign Bengie Molina, but that will only make them worse, not better. This can't be the end of the Mets' offseason, else the money spent on Bay -- which is likely to be better spent now than in the final year or two of the deal -- will go for naught.
The Bay signing leaves Matt Holliday as the only impact hitter on the market, and he won't sign for a penny less than the five years and $80 million or so Bay probably will get when the fifth year vests. At the same time, his market is limited, and if it's really just St. Louis chasing him, I would expect the two sides to play chicken for another month. This deal also increases the chances that Johnny Damon has to return to the Yankees with his tail between his legs and take a one- or two-year deal at a big cut from his 2009 salary.