This may be a stupid question, but how do we know what the defense rating means?  I mean maybe somebody has a lot more time than I do to go through and see points against certain players, but in looking through steals numbers for guards I am not seeing a big difference from a guy rated 90 to a guy rated 30.  I know steals are not the only indicator of defense, but it just seemed odd to me.

Steals are largely dependent on speed. If you were to break down opponents' shooting percentages against a player with a DEF rating of 30 compared to one with a rating of 90, you'd see the difference. It confuses me too that steals aren't really related to DEF, but I hope that answers your question.

Steals are very dependent on speed.  That may be why those numbers are a little wacky.

To tell if defense matters look at a teams FG% allowed.   Mine are generally in the low 40's.  My NYU team which has ELITE d3 defense is 39.4%.   I like defense.

I've also noticed it for independant players.  Yes occasionally someone will shoot good against a 95 D guy, but overall the D does make the guy shoot poorer.  I can't be exact because I am going starters vs starters and this wont include a players shooting stats against the sub.  But I do think it lowers the shooting pct on the opposing player.  I see it quite a bit with my 95-100 D players.