At one point this season, the Tigers were ranked as the number one defensive team in the league according the Ultimate Zone Rating statistic found at FanGraphs. Their defense is still strong but has slipped a bit as the season has progressed. They are currently 23.5 defensive runs saved above average with ranks them fourth in the American League:
Despite the defensive regression, they are still way ahead of last years unit which was 39.1 runs saved below league average. The difference of 62.6 runs between 2008 and 2009 is worth an estimated six additional victories over a full season. A position by position look follows:
Miguel Cabrera is ranked about average (UZR=+0.5 runs saved above average).
Placido Polanco's 7.2 UZR is second in the league to Dustin Pedroia. He is ranked above average by the plus/minus statistic listed at Bill James Online as well but not by as much (+2).
Adam Everett is ranked close to average on UZR (0.5). That he is only average defensively is a concern given that he has become a black hole at the plate.
Brandon Inge is an excellent defender by either measure: +9.5 on UZR and +10 on +/-.
Curtis Granderson has a -2.8 UZR and +1 +/-. It's really looking like Curtis is not the defender he seemed to be in 2007 when he ranked near the top of the league on most defensive measures. Last year, he was significantly below average so it's been two straight years of average at best for Granderson defensively.
Corner outfield spots
With the revolving door in left and right this year, there isn't enough data on specific players here. Clete Thomas is looking stong in right field according to Ultimate Zone Rating (+10.3) but has a +/- of -1 which is an example of how volatile these defensive measures can be with a limited sample. Magglio Ordonez is a little below average on both measures.
Overall, the Tigers are very strong at second and third, possibly above average in one corner outfield spot with Thomas and about average everywhere else. There is no position where they are substantially below average. While they are not looking as stellar as they did early in the season, defense still maintains a relative strength.