As the inevitably parochial MVP debates heat up in the American League, it’s worth keeping in mind that one of the prime contenders, Yankees third baseman Alex Rodriguez, may have a forthcoming appointment with history. If horse sense prevails, Rodriguez will certainly triumph over the inferior (though worthy) David Ortiz, but the Yankee superstar has in his sights a more substantial honor.

Rodriguez has compiled a batting line this season of.321 AVG/.421 OBP/.600 SLG in 629 plate appearances. He’s also tied for the league lead with Ortiz with 41 home runs, and fourth in RBI with 111. According to Value Over Replacement Player (VORP), a Baseball Prospectus statistic that measures how many runs a player is contributing with the bat above what the team might get from a readily available “replacement-level” talent (like Bubba Crosby), Rodriguez has been the best hitter in the AL this season. However, even that honor may not do justice to the season he’s cobbling together. Indeed, Rodriguez’s season may wind up as the best ever by a third baseman.

If paces hold, Rodriguez will wind up with a VORP of 98.4 for the season. That would be good for second on the all-time list for third sackers. (See accompanying chart.) Populating the rankings are first-ballot Hall of Famers like Brett and Boggs (though, strangely, no Mike Schmidt), genuine luminaries of the game like McGraw, and seasons ranging from 1887 to the present day. It’s worth noting that just missing the list is Rodriguez’s manager Joe Torre, whose 1971 season ranks as the 12th best hitting performance ever at the position.

Anyhow, as you can see, Rodriguez is on pace to have the best offensive season ever by an AL third baseman and come within hailing distance of Chipper Jones’s historic 1999 VORP of 105.8. That’s already rarified air, but it’s also possible that Rodriguez could make up that ground between him and Jones. Left on the Yankee schedule are the Devil Rays (one game), Orioles (eight games), Blue Jays (six games), and Red Sox (three games). That means Rodriguez will be facing pitching staffs and defenses that rank, on average, ninth in the AL in runs allowed. So he’ll get to enjoy, for the most part, a run of teams that are subpar in terms of keeping runs off the board. To boot, Rodriguez will close the season with three games in Boston’s Fenway Park, which is a terrific environment for right-handed hitters.

As for recent trends in performance, they also favor a numbers spike for Rodriguez. A-Rod has authored a batting line of .327 AVG/.429 OBP/.630 since the All-Star break (compared to a modestly inferior pre-break line of .317 AVG/.416 OBP/.582 SLG). Even more impressive, he’s batting .331 and slugging .665 since August 1.

However, even if A-Rod fails to make up the ground separating him and Jones, or even falls off his current pace, you can still muster a case that his season is the best ever for a third baseman. That’s because of his defense. Advanced, zone-based defensive metrics don’t really do justice to the left side of the Yankee infield because they almost always play shaded toward second base. This hurts both Rodriguez and Derek Jeter in statistics that track balls hit into each defender’s fielding zones. Nevertheless, scouts, anecdotal accounts, and Rodriguez’s pre-Yankee defensive numbers will tell you he’s a stellar defender, a Gold Glove-caliber shortstop now playing a less demanding position.

Factor in Rodriguez’s advantages with the glove, and it’s reasonable to push him past Jones and anyone else on the above list. In all likelihood, Rodriguez ranks among the near-great defenders at the position, a notch or two lower than the likes of Mike Schmidt, Brooks Robinson, and Clete Boyer. That’s certainly enough to make up whatever offensive gap that might exist between him and Jones, who for much of his career has been no better than average with the glove.

So can we call Rodriguez’s 2005 season the greatest ever by a third baseman? Accounting for his offensive and defensive contributions, yes, we can.

Mr. Perry is a writer for Baseball Prospectus. For more state-of-the-art commentary and information, visit their Web site at www.baseballprospectus.com.