Note: Go to the bottom of the table for a more complete explanation of how Aaron's QB rating system works.

One of the most important parts of these ratings is the adjustment for opponent. Passing for 300 yards on the Saints is not the same as passing for 300 yards on the Steelers. So this week, I thought I would switch things around and show the rankings of the best and worst defenses in terms of PAR given up to opposing quarterbacks.

This is especially noteworthy this week because the two biggest quarterback performances were significantly affected by the quality of the opposing defense. If we don't adjust for opponent, Donovan McNabb's 464 and 5 TDs against Green Bay was easily the best performance, followed by Carson Palmer, Kerry Collins and Peyton Manning. But Green Bay has given up more big passing games than any other team, and the Ravens have been the best defense in football. When you adjust for that, Palmer's game actually scores as more valuable than McNabb's game, with Manning third and Collins a bit farther down because a big offensive performance came against Kansas City.

Carson Palmer's big day also shows that, just like the quarterbacks they face, great defenses can have bad days and bad defenses can have surprisingly good days. I'm guessing that fantasy football players everywhere did a double take watching the ticker at the bottom of the screen as Buffalo and Miami racked up the points and St. Louis and San Francisco had a defensive struggle. It was like "Freaky Friday," only without Lindsay Lohan.

Anyway, here's a list of this season's 10 best and worst defenses, ranked by how many Points Above Replacement they've given up to opposing quarterbacks. The difference here is that instead of adjusting for the defense, the numbers are adjusted for the opposing offenses. After all, you don't want to penalize those poor AFC South teams that have to face Peyton Manning twice.

Top pass defenses    Worst pass defenses
Team     PAR         Team      PAR
BAL    -14.7         GB        86.9
PIT    -11.5         NO        86.3
NE      -6.5         STL       80.6
TB      -4.7         SF        80.0
CHI     -3.6         MIN       77.5
DEN      3.2         OAK       69.3
TEN      5.4         DAL       63.9
PHI     11.2         KC        55.3
WAS     11.8         IND       41.7
BUF     13.9         JAC       40.7

*Not counting Monday Night Football this week.