Expectations about what Johan Santana is going to do in Shea Stadium couldn't be higher. But those anticipating Santana to put up a Bob Gibson 1968 type of season are probably in for a disappointment.

Yes, there is no designated hitter in the National League, and Santana will get to face off against a less talented group of offenses than in the AL. And Shea Stadium is a favorable environment for any pitcher. But Santana also had some advantages working for him in Minnesota. The Metrodome had played as a moderate pitchers' park in recent years -- it depressed offense by around 16% last season -- and Santana has generally had the luxury of pitching in front of good defenses. Moreover, Santana may have declined slightly off his 2004-06 peak. While he has always given up a fair number of fly balls, last year that tendency began to catch up with him, as he gave up a career-high 33 home runs.

All told, Baseball Prospectus's PECOTA projection system forecasts that Santana will get his ERA back below the 3.00 mark. He also stands to pick up an extra win or two in front of the Mets' strong offense. That's still very good, but the marginal gain may be less than you'd think -- PECOTA expects Santana's ERA to be 38 points lower with the Mets than it would be with Minnesota.

On the other hand, this is still an exceptionally good fit between player and team. BP's studies have shown that there is a tipping point at about 90 wins -- a team that wins 90 games usually makes the playoffs, and a team that wins fewer than 90 games usually misses out. The Mets found out about this last season in the most difficult fashion imaginable, stalling at 88 wins and blowing a playoff spot on the last day of the season. But Santana, who should replace the underachieving Mike Pelfrey or the overaged Orlando Hernandez in the rotation, should provide the Mets with an immediate 5-6 win upgrade. That will differentiate them from the large cluster of National League teams -- the Dodgers, Rockies, Diamondbacks, Cubs, Brewers, Braves and Phillies -- that project in the 85-90 win range, and there will be no excuse for their failing to make the playoffs this time.

One last thing to consider: This move is all about 2008. That's the only year remaining on Santana's contract. The Mets will presumably sign Santana to an extension, but it will require them to pay market price, since Santana knows he would get plenty of traction as a free agent. Generally speaking, it's a mistake to trade several prospects for one year of below-market value performance from a superstar. But the prospects the Mets gave up are marginal enough -- and the financial bounce from a post-season run projects to be large enough as the Mets try and ramp up momentum heading into their new ballpark, Citi Field, in 2009 -- that this may well prove to be an exception.

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