People used to say that Alex Rodriguez wouldn't be considered a True Yankee until he won a World Series. Well, he did that last year -- and had a .973 OPS in the World Series, and 18 RBIs and 7 HRs in 15 post-season games that year -- but he's still not considered a True Yankee.
He has now played more games as a Yankee (1,028) than he did as a Mariner (790); he has over 1,000 more plate appearances as a Yankee than he did as a Mariner. He has scored over 100 runs more as a Yankee than as a Mariner, has 171 more hits, 246 more RBIs, 79 more home runs as a Yankee. He has accumulated more Wins Above Replacement as a Yankee (40.9) than he did as a Mariner (37.1). His only World Series ring, so far, came as a Yankee. He has two MVPs as a Yankee, one as a Ranger, and surprisingly, none as a Mariner. He will undoubtedly go into the Hall of Fame as a Yankee.
But will he ever be considered a True Yankee?
The best way to become a True Yankee, of course, is to come up through the system (Derek Jeter, Don Mattingly, Mariano Rivera, Robinson Cano) and never leave*. If you do that, you're in.
*(Note: Some players can retain True Yankee status even if they leave the team. That's The Andy Pettitte Exception: If a True Yankee goes to another team, he can resume True Yankee status by not being too good with his new team, then returning to the Yankees and being good again. Hideki Matsui: The porch light is still on, my friend!)
A-Rod didn't come up through the system, but wait a minute -- there are some players considered True Yankees who didn't come up through the system either. That's The Paul O'Neill Clause: A player who improves dramatically once he puts on the pinstripes can assume True Yankee status. (See also Brosius, Scott. Nick Swisher appears to be on this track.) It helps if you arrive via trade as opposed to free agency, so we don't have to hear all that crap about how we just bought the highest-priced player. (Sorry, Mark Teixeira and C.C. Sabathia.)
The problem with A-Rod -- he was already a superstar before he got here. Like Roger Clemens or Reggie Jackson, if you're a marquee player before you come to New York, you'll never be good enough. Hit a home run? That's what why we brought you here. Strike out? You suck!
Oh, we'll cheer when you hit a home run -- but a few 0-for-4s and you're a bum again.
Sorry, Alex. I guess you'll just have to be happy with Cooperstown.