When a team is as good as the Boston Red Sox are, there’s little need to dwell on its mistakes. No team gets everything right. Still, it’s hard not to imagine what would have happened if the Sox had never traded for Josh Beckett. How good would they be?

The absurd thing about the question is that Beckett has this year, at 27, become everything anyone ever thought he could be. For years, Beckett was a good pitcher, and one of the most frustrating in the game. His fastball and hammer curve gave him pure stuff as good as anyone in the game, and no one who saw him dominate the Yankees in the 2003 World Series could question his competitiveness, but the pieces never quite fit. When he was good he suffered minor injuries; last year, when he was finally more or less healthy for an entire year, he wasn’t any good.

This year, he’s become an ace. His record is 15–5 with a 3.24 ERA, and if anything, that understates how good he’s been. Perhaps most important for the Red Sox, his strikeout-to-walk ratio stands at 4.83, more than double last year’s and well above 2.86, his previous high. It’s a sign that he’s not just having a great year, but that he’s matured and become a different pitcher, and if the improvement keeps up, he’ll contend for Cy Young awards for years to come. Beckett is owed just $20 million over the next two years, and the Red Sox hold a $12 million option on him for 2010, a preposterous bargain in the current pitching market. And for all this, you have to think that the Red Sox would, even if they’d never admit it, undo the deal that brought him to Fenway if they could.

That, of course, is because of who they traded to get him — shortstop Hanley Ramirez, who at 23 is hitting better, relative to his position, than anyone else in baseball. A first baseman his age hitting .341 AVG/.393 OBA/.571 SLG with 37 steals, following on a tremendous rookie campaign, would be regarded as a priceless asset. A shortstop that does that, even one as lousy afield as Ramirez, is irreplaceable. Since integration, the only shortstop 23 or younger that has ever posted a batting average or slugging percentage that high is Alex Rodriguez.

Making things worse is that Boston shortstop Julio Lugo, in the first year of a four-year, $36 million contract, is hitting .233/.295/.337. I doubt there’s a Red Sox fan alive who doesn’t look at the man every inning and every at-bat and curse him while imagining Ramirez whacking doubles off the Green Monster.

It was a fascinating deal when it was made, it became more so when Ramirez unexpectedly emerged as a full-blown star last year while Beckett struggled, and it’s still more so now that you could make a case for Beckett being the best pitcher in the American League this year and Ramirez being the bestpositionplayerintheNational League this year. How much impact, though, has it had on the Red Sox this year?

Imagine an alternate world where the trade had never been made. In this world, Mike Lowell, the Sox third baseman who came over from Florida in the deal because the Marlins didn’t want to pay his salary, is still playing in Miami; Boston first baseman Kevin Youkilis is playing third base and hitting as well as he is now. Ramirez is at short. The Sox have an average first baseman, say Sean Casey, to whom they’re paying $7 million a year, and to fill the spot Beckett takes in the rotation they have an average pitcher, say Jon Garland, to whom they’re paying $13 million.

Oddly enough, this is effectively a wash. Having Casey/Youkilis on the corners rather than Lowell/ Youkilis would cost about 10 runs on offense; having Garland rather than Beckett in the rotation would cost around 25 runs in pitching. Having Ramirez rather than Lugo would represent a gain of around 70 runs on offense. That’s a gain of 35 runs to the Red Sox. But then you have to factor in defense, and while that’s really hard to pin down, the difference at third base would be worth a few runs, while the difference at shortstop would be enormous, probably somewhere from 10 to 20 runs. Ramirez is very bad, and Lugo is good. Add it all up, and the Red Sox would be just a win or two better with Ramirez. They’d be $9 million or so richer, too, and off the hook for Lugo’s ridiculous contract, but that doesn’t count so much for such a rich team.

In the end, this deal might well prove to be a debacle — Ramirez could go on to the Hall of Fame, while Beckett might prove to be just a solid pitcher having a career year. On the other hand, Beckett might win a second World Series MVP award while Ramirez might end up moving to second base because of his defense, and following the Carlos Baerga career plan. Who knows? In the short term, this has been no disaster, and that’s with Ramirez having exceeded the wildest expectations. The lesson? Maybe teams ought not to listen to people like me shrieking about building from within with young prospects. Trade one for a young pitcher, watch him slug nearly .600 while playing shortstop, and you still won’t come out all that far behind if you manage things right. Potential counts for a lot, but even when it’s fulfilled, it only does so much.

tmarchman@nysun.com