By one measure, the Tampa Bay Rays have been the best team in baseball to date. They have the top third-order record in the game, better even than the two teams they’re currently chasing in the AL East, or the Los Angeles Dodgers in the NL. The Rays are doing it with offense-fourth in MLB in Equivalent Average-this season, as opposed to last year’s team that played outstanding defense. The 2009 Rays have just a mid-pack squad as measured by Defensive Efficiency, a significant dropoff from last year’s highly publicized improvement. The loss of Akinori Iwamura has played a part in that, but for the most part we’re seeing regression by the same set of players who took the field a year ago.

The Rays’ offense is an incredibly strange beast, a mix of players who are over- and underperforming projections by a wide amount, all leading to about the same end performance as you’d expect from them collectively. On the good side, you have Ben Zobrist and Jason Bartlett, projected for EqAs of .259 and .243 respectively, but clocking in with career seasons of .333 and .320. Those numbers balance out the disastrous season Dioner Navarro is having (.205 EqA, .256 projected) and the disappointing work being done by B.J. Upton (.257/.292) and Pat Burrell (.257/.293). On balance, the Rays are about as good as you’d expect them to be, and they can be expected to do about the same the rest of the season as everyone meanders back to their level. The X factor here is Zobrist, whose All-Star selection I panned just a few short weeks ago; he’s hitting .379/.463/.500 since the day he was picked. The longer a “fluky start” goes, the more you have to consider the possibility it’s a real change in ability. I remain a bit skeptical, but his performance speaks loudly.

The difference in the Rays’ run prevention this season is entirely the change in the defense. They’re giving up essentially the same rates of walks and home runs, and striking out the same number of batters. More hits are falling in, and therefore more runs are being scored. The back end of their rotation has been hit the hardest, with both Andy Sonnanstine and Scott Kazmir seeing their ERAs push 7.00 as a result of upticks in their home-run rates and BABIP marks. The Rays’ bullpen has been a work in progress all season long, as injuries and command problems have forced Joe Maddon to shuffle roles and usage patterns. He seems to have settled upon J.P. Howell as a traditional closer, although that may change down the stretch.

The point is that the Rays are a very good team with some flaws, most notably at the back of the rotation and at catcher. Those are two positions, as it turns out, that can be fixed by making a major trade for a player. Roy Halladay is the most obvious solution to the rotation issue, and the Rays, with David Price, could put together arguably the most attractive package for the Blue Jays‘ ace. Chasing a catcher could be as simple as contacting Mark Shapiro of the Indians, who has Victor Martinez heading for free agency after 2010, and is on the fence between contending next season and starting over. The Rays could clearly help that decision along, as even behind Price they have a wealth of pitching prospects, as well as an athletic outfielder in Desmond Jennings who would fill a real hole for the Tribe.

But with all that said, there’s no way the Rays should be a buyer at the trade deadline. It’s not that they couldn’t catch the Red Sox or Yankees, or that if they were to do so, they couldn’t make another deep run in October. The numbers don’t lie: the Rays have played just as well as their counterparts to date, with only some underperformance relative to underlying expectations on offense keeping that from showing up in the standings. However, that gap exists. The Rays are trying to make up a four-game deficit on what should be the best team in baseball, and a 5½- game gap on one of the other candidates for that title. Both of those teams have either improved themselves-see the Red Sox acquiring Adam LaRoche and bringing up Clay Buchholz-or have the means to do so. There’s little in their performance to date or in their construction to indicate that they will be fading, and if anything, they both have room to improve.

The main difference between the Rays and the two teams they’re chasing is the expectation of future success. The Rays have a young core in Upton, Price, Matt Garza, James Shields, and Evan Longoria that is on the upswing and will be the starting point for a championship-caliber club for a long time to come. Those five players are going to be a massive competitive advantage for the Rays, and breaking up that core for a short-term boost that is likely to be unsuccessful-adding Halladay makes them two wins better over 10 weeks, and they need at least four wins to make up the gap on the Sox-isn’t the best thing for this franchise. Of the teams chasing Halladay, the Rays are the one least likely to be able to retain him, as the team’s run to the World Series last season has not changed their situation in Tampa enough to make them a player for the game’s top free agents. (They’re averaging fewer than a thousand additional tickets sold per game this year.) He would be a rental, and possibly a very short-term one if they’re unwilling to pay one player 20 percent or more of their payroll next season.

This is the hardest team in MLB to make this call on, because of the combination of how good the current team is, how well the best available players match up to their needs, and how much talent is in place to be used either in trade or in future seasons. With Halladay instead of Price, the Rays would be about two wins better down the stretch this year, and maybe five wins better next season. The Rays with Halladay in 2010 might well be the best team in baseball. That, in fact, is the best argument for them to pursue him, or Martinez for that matter: the impact on the 2010 team. However, when you look at the long-term opportunities here, the ability of the Rays to pay premium talent, and most importantly, the Rays’ realistic chances in 2009, you can’t conclude that they should break the talent bank for a major acquisition.

For most teams, the buy/sell decision is a binary one. The Rays are an exception here, as they have no older talent having big seasons, no impending free agents with trade value to convert. There’s no reason for them to be a seller, as the players they have whose trade value is peaking, such as Zobrist, Bartlett, and Howell, are unlikely to bring back enough to warrant a deal. I’m not even sure there are minor moves to be considered; an upgrade at catcher short of acquiring Martinez would be nice, but the dropoff after him is something like Gregg Zaun. The team has plenty of in-house options for the rotation and bullpen, and if Akinori Iwamura does come back earlier than expected, that will be a boost to the depth as Zobrist or Gabe Gross loses starts.

If any factor were different-if the Rays were closer to or in first place; if they were seeing more of a bounce from last year’s success; if it were a few weeks earlier; if their future didn’t look quite so bright-there would be a great case for building a Halladay offer around David Price. As it stands now, though, the best thing they can do is keep their roster intact with the knowledge that their time is just about here.