Defense And Fantasy

[RotoValue]

I'm wondering if anyone has experience with leagues using defensive categories. If so, what do you use? What works well, what doesn't?

It seems there's some symmetry in an old-school 4x4x4, using ERA/WHIP/W/S for pitching, Avg/HR/RBI/SB for offense, and PO/AST/DP/Pct for defense. I'd restrict rosters to at most one per position (no utility slots), but I'm sure there are other ways to play.

Tom Tango suggested this:
http://tangotiger.com/index.php/site/comments/fan-tasy-rules-idea-that-includes-fielding-games-played-at-premium-position

Remove positional eligibility altogether (i.e. all offensive players are Util), but giving players credit for playing games at harder positions: 1 point per game at 2B/3B/CF, and 2 points for SS/C.

What variations have people tried, and what do they like?