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GLENDALE, Ariz. -- If there's one thing we know about the NFL, it's that any given week can produce a fair share of surprises.

This Sunday was a perfect example, especially for those who enjoy upsets. You had some games nobody would've picked (such as Arizona over Pittsburgh and Cleveland over Baltimore). You had others that made some sense (such as Atlanta defeating a Houston team without injured wide receiver Andre Johnson and the Bills taking down the listless New York Jets).

And finally, you had the contests that were shockers (such as Detroit scoring 34 points in a fourth-quarter comeback against Chicago). It was enough to make any logical person shake his head in disbelief.

But I won't try to make too much sense of all that. Instead, I'll focus on my 10 observations from Week 4:

1. Cardinals' defense delivers

Everybody is talking about the alternating quarterback strategy in Arizona -- Matt Leinart and Kurt Warner both played again in a 21-14 win over Pittsburgh -- but people also need to notice what's happening with the Cardinals' defense.

The Steelers' offense had been averaging 32.3 points and a league-high 198.3 rushing yards per game entering Sunday's game. However, Pittsburgh learned that the Cardinals can shut people down when they're committed. They have the talent -- thanks to players such as defensive tackle Darnell Dockett (three sacks and a forced fumble against the Steelers) -- and they have the motivation that comes from having blown too many games in the past.

"I've been here for four years, and we've waited a long time for this defense to come together," defensive end Antonio Smith said after the Cardinals allowed just 77 rushing yards against Pittsburgh. "Now people are seeing what we really can do."

2. Change for the better

If the Chiefs are going to win more games this season, coach Herm Edwards will have to open up the offense as he did in the 30-16 win over the Chargers.

These weren't the same Chiefs that scored just 26 points in their first three games. This time around, Kansas City actually looked as though it had some semblance of a dangerous passing attack, with rookie wide receiver Dwayne Bowe dominating the San Diego secondary (eight receptions, 164 yards and a 51-yard touchdown catch). It was a significant change for a team that had been struggling with the conservative play calling of offensive coordinator Mike Solari since the season began.

In fact, Pro Bowl running back Larry Johnson should be the happiest player in the Chiefs' locker room. If Bowe can remain a consistent threat -- which is something the Chiefs haven't had at receiver in nearly a decade -- there should be fewer reasons for defenses to focus all their attention on Johnson.

3. Paying the Pryce

It's becoming quite apparent that the Ravens' current defensive issues have plenty to do with the broken left wrist that has sidelined defensive end Trevor Pryce. Just check out the stats from Baltimore's 27-13 loss to Cleveland. The Ravens didn't have a single sack in that contest. In fact, they have only six for the entire season.

Say what you will about all the stars on the Baltimore defense, but the unit relies heavily on the strength of its pass rush. Without Pryce -- who led the team with 13 sacks last season -- the Ravens don't have a lineman who can dominate opponents on any given down. The free-agent departure of Adalius Thomas also left the team without another proven pass-rusher who could create mismatches for others.

Even outside linebacker Bart Scott (9.5 sacks in 2006) has been unable to blitz as much this season. So until Pryce returns in about three weeks, don't expect the Ravens' woes to vanish.

4. Running in place

Cedric Benson hasn't done much to prove that trading Thomas Jones was a smart move for Chicago. After gaining just 50 yards on 15 carries in a loss to Detroit, Benson has 239 yards this season and is averaging just 3.2 yards per carry.

This isn't exactly what the Bears expected from a player they selected fourth overall in the 2005 draft. And what's even scarier is that Benson will only see more teams lining up to stop the Bears' running game now that Brian Griese has shown he can throw interceptions just as frequently as his predecessor, Rex Grossman.

In fact, I'd probably be even more pessimistic about Benson's future as a feature back if some scouts hadn't persuaded me to stay patient. One AFC personnel director said Benson is really the kind of back who plays better the more he touches the football. If that's the case, I'd like to see what he could do with 20 or more carries in a game, which is something that has happened only once this season (when he gained 101 yards on 24 carries against Detroit). Until that point, I'll remain doubtful that he's a special runner.

5. Bucs lose a Cadillac

I wouldn't write off the Bucs after they lost running back Cadillac Williams to what looked like a severe knee injury in a 20-7 win over Carolina. Although Williams is a key figure in the Tampa Bay offense, efficiency has been the most valuable factor in the team's 3-1 start.

After Sunday's game, the Bucs' turnover ratio is plus-4, and much of that has to do with the play of quarterback Jeff Garcia. He hasn't thrown an interception this season.

6. Seattle's still standing

The Seahawks sent a strong message to the rest of the NFC West in Sunday's 23-3 win over San Francisco. I believed the 49ers were ready to make a run at the division title, but a blowout loss at home doesn't say much about their stature right now.

First, the Seahawks roughed up quarterback Alex Smith (who left the game with a shoulder injury after three plays), then they beat down backup Trent Dilfer for the rest of the game. (The Seahawks registered all six of their sacks in the first half.).

Let's just say the 49ers knew where they stood at the end of that contest. If they want to take down the Seahawks in that division, they simply can't get pushed around in their own backyard.

7. Rapid rebound

Give Falcons quarterback Joey Harrington credit: He got the message when the Falcons signed Byron Leftwich a couple of weeks ago.

Over Atlanta's past two games -- including Sunday's 26-16 win over Houston -- Harrington has completed 74 percent of his passes for 584 yards with four touchdowns and one interception. That's pretty good for a quarterback who had earned the ire of coach Bobby Petrino after taking 13 sacks in the Falcons' first two games.

8. Raiders on the run

You had to be impressed with the Raiders' running game in their 35-17 win over the Dolphins. Oakland gained 299 yards on the ground, with backup Justin Fargas supplying a career-high 179 yards after he replaced injured LaMont Jordan.

If the Raiders can get that kind of production from their backfield on a weekly basis, they just might surprise a few people this season. They already had Jordan averaging 116.7 yards a game entering Week 4, plus they have Dominic Rhodes returning from a four-game suspension after this week. With that kind of ground game, Oakland can keep the pressure off its quarterbacks and allow an underrated defense to stay fresh.

9. Cautious optimism

Let's keep things in perspective now that rookie Bills quarterback Trent Edwards has enjoyed an impressive debut. Yes, he deserves plenty of credit for his performance in a 17-14 win over the New York Jets (22-for-28, 234 yards and one touchdown). But do I think this is the start of a quarterback controversy in Buffalo? No.

Most coaches and scouts will say it's hard to evaluate a new quarterback off a debut. That's because facing a quarterback for the first time is comparable to a batter facing a pitcher in baseball for the first time. The advantage usually goes to the signal-caller until defenses learn his tendencies, something that usually takes about four or five weeks. So although Edwards certainly proved he has a shot at a bright future, he'll see his share of challenges in the near future.

In fact, all he has to do is ask the man he replaced -- injured quarterback J.P. Losman -- how quickly things can change after a strong start. Losman excited fans while leading the Bills to a season-opening win in his first start back in 2005. Three weeks later, he was benched.

10. Familiar faces, new places

Sunday wasn't just a day for upsets. It was a day for some coaches and players to face their old employers. Arizona Cardinals coach Ken Whisenhunt and offensive line coach Russ Grimm certainly enjoyed their victory over Pittsburgh, the team they helped win a Super Bowl two years ago.

Raiders quarterback Daunte Culpepper also got some revenge on the Dolphins (three rushing touchdowns and two passing), and Jamal Lewis did enough (23 carries, 64 yards, one touchdown) to help Cleveland beat Baltimore.

The only guy who didn't get to beat up on his old team was Houston's Matt Schaub. He saw Atlanta's Harrington upstage him.

Jeffri Chadiha is a senior writer for ESPN.com.