Tom Brady goes down, Matt Cassel steps in. No problem.

Matt Schaub goes down, Sage Rosenfels steps in. Umm, Houston, we have a problem.

Now, more than ever, quarterbacks determine the fate of their franchise. This week, NFL.com examines why teams will do just about anything to acquire one.

Monday: Why quarterbacks matter
Busy offseason shows importance of position
» Wyche: Offseason showed QBs matter | Photos
» Kirwan: Rankings | George: Three for the show
» Video: A QB's worth? | Emphasis on QB

Tuesday: Finding "The Guy"
How teams find (or don't find) the right QB.
» Wyche: Looking for Mr. Right ... or Mr. Right Now
» Carucci: Real secret behind QB success
» Brooks: Why some college stars fizzle in NFL
» NFL Network crew debate: Brady or Peyton?

Wednesday: Why it's so hard
Some teams never find the guy; some never get it
» Wyche: What makes the great ones so great
» George: Lead and you will succeed
» Deion and friends: What makes a great leader?

Thursday: Making it easier
What teams have done or can do to help their QB.
» Wyche: Why young QBs are on a short leash
» Brooks: Wide-open schemes help QBs | Trends
» Carucci: Protect and serve ... the QB

Friday: Counter-moves
How defenses have responded to rise of the QB.
» Wyche: How to take down QBs | Under pressure
» Kirwan: Why teams go 3-4 | Getting defensive
» George: Hunting Wildcat is top priority

» Team-by-team previews and predictions

NFL Network season preview:
» Season preview roundtable, Sept. 9, 6 p.m. ET
» NFL Total Access' preview, Sept. 9, 7 p.m. ET

Or should we say, had a problem? When Schaub went down in Week 9 last season, the Texans were on a roll having scored 27, 27, 29, 28 and 35 points in five consecutive games and winning three straight. When Rosenfels replaced him, Houston lost three in a row, and for all intents and purposes, was done in the ultra-competitive AFC South.

The Texans weren't the only ones doing the quarterback shuffle last season. Only 16 quarterbacks started all 16 regular-season games. In other words, half of the teams in the NFL had to go to their second or third quarterbacks at some point because their starter got injured or failed to deliver and had to be replaced. In all, 53 different quarterbacks started a game in 2008, one season removed from an NFL-record 64.

How important was having a 16-game starter last year? Of the 12 teams that made the playoffs, only one -- Minnesota -- had multiple starters after Week 1; Tennessee made its switch by Week 2 and stayed with Kerry Collins the remainder of the season.

Every team has already asked itself this question as final roster adjustments are being made to get down to the mandated 53-man roster limit by Saturday: If our starting quarterback is lost for any significant part of the season, what happens to our team?

The answer could be the difference between, well, New England (11-5 record, nearly making the playoffs) and Houston.

Quarterback is the most important position on the football field, but making sure you have the position properly supplied heading into the season is a challenge for most teams.

The chart below was used to quantify the quarterback depth of each roster entering the 2009 season.

Points -- Explanation
9-10 -- Top 10 signal-caller in the league.
8-9 -- Ranked 11-16 and in the top half of the league.
7-8 -- Ranked 17-22 and could win with a dominating defense.
6-7 -- Ranked 23-28 and needs a big supporting cast around him.
5-6 -- Ranked 29-32 and not good enough but starts on a poor team.
4-5 -- Backup who can win coming off the bench with starter experience.
3-4 -- Backup who could go .500 on a limited basis.
2-3 -- Backup with a special trait (i.e. speed) or a first-round pick in the wings.
1-2 -- Backup who can take a snap and not embarrass himself.
0-1 -- Backup who knows system to finish a game, at best.

A team in great shape would have their starter score between 8-10 points, their backup between 4-6, and their third-stringer, whom they hope not to count on much over the course of the season, with a point or two. Any team with a combined score of 13 or higher should be in good shape. In my evaluation, there are 14 such teams.

Rating NFL quarterback depth
Rk
Team
Points
Quarterback depth chart
1.
17.8
Donovan McNabb, Michael Vick, A.J. Feeley (Kevin Kolb)
Comment: McNabb is a top quarterback with excellent weapons. Vick, as a former starter in Atlanta, is the best backup in the league. Feeley has 23 career starts and has won in the Eagles system. Depth is not a concern here.

2.
16.0
Kurt Warner, Matt Leinart, Brian St. Pierre
Comment: Warner got his team to the Super Bowl with an aggressive pass attack and Leinart can run this team as well. Saint Pierre knows the system, which means the Cardinals won't abandon the pass with an injury.

3.
15.7
Tony Romo, Jon Kitna, Stephen McGee
Comment: This is the year that Romo will be evaluated as a leader. With Terrell Owens gone, he now owns the huddle. Kitna is a top backup and he should help Romo on the sideline. A strong run game helps both quarterbacks.

4.
15.5
Comment: Rivers was the highest-rated quarterback in the NFL last year and only threw 11 picks in 478 attempts. Volek can move the team and win games if called upon and Whitehurst would not embarrass himself if asked to play.

5.
15.4
Drew Brees, Mark Brunell, Joey Harrington
Comment: Brees does not get sacked often (once every 49 attempts), which means a fifth straight 16-start season could be in the cards. Brunell and Harrington offer starting experience as the backups.

6.
15.2
Ben Roethlisberger, Charlie Batch, Dennis Dixon
Comment: Roethlisberger's Super Bowl performance moves him into an elite class. Batch knows the offense inside out and could keep the team afloat if he had to play for a month. Big Ben started 19 games last season but has had his share of bumps and bruises.

7.
15.1
Brett Favre, Sage Rosenfels, Tarvaris Jackson (John David Booty)
Comment: Favre changes everything for the Vikings. Before he injured his arm last year he was a top-rated quarterback. The Vikings will keep him on limited throws all season. Jackson has already led the team to the playoffs and Rosenfels has won coming off the bench.

8.
14.6
Jake Delhomme, Josh McCown, Matt Moore
Comment: Yes, Delhomme threw five intereceptions in Carolina's playoff loss last season, but he led the Panthers to 12 wins. He didn't miss a start in 2008 coming off Tommy John surgery. McCown has starter experience and Moore is underrated.
Rk
Team
Points
Quarterback depth chart
9.
14.5
Comment: If you're strictly grading the league's starters, Manning lands in the top two. But Manning's backups, and their lack of experience, drops the group as a whole. If Manning were to get injured, things would change radically for the Colts.

10.
14.4
Tom Brady, Andrew Walter
Comment: Brady is the league's top quarterback in the eyes of most evaluators, but he is coming off a serious knee injury. His backup now is Walter (for the moment) after the Patriots parted ways with Kevin O'Connell, their 2008 third-round pick. If Brady goes down again, the Pats could be in trouble.

11.
13.6
Eli Manning, David Carr, Andre Woodson
Comment: Manning is more than a system quarterback and has proven he can win a Super Bowl. His backup, Carr, provokes a lot of questions because of his shaky past. Woodson, who spent last season on the practice squad, isn't ready.

12.
13.3
Comment: Hasselbeck looks back to his 2007 form when he had 28 TD passes and just 12 interceptions. He has solid weapons, which should help him. Wallace now has starter experience and Teel is worth working with as a developmental player.

13.
13.2
Kerry Collins, Vince Young, Patrick Ramsey
Comment: Collins solidified the position but he is not asked to do much in the passing game. Vince Young looks lost at times, and Ramsey, with his starting experience, gives the Titans a possible answer if Young stumbles.

14.
13.1
Chad Pennington, Chad Henne, Pat White
Comment: Pennington doesn't excite the average fan but he is accurate, rarely makes mistakes and led the Dolphins to a division title last year. Henne is a fast-rising star and White brings a special dimension to the Wildcat.

15.
12.8
Carson Palmer, J.T. O'Sullivan, Jordan Palmer
Comment: If Carson Palmer can stay healthy, then the Bengals have a top quarterback situation. But health has been an issue for him in the past. O'Sullivan has starter experience and Jordan Palmer won't embarrass himself if he has to play.

16.
12.6
Jay Cutler, Caleb Hanie, Brett Basanez
Comment: Acquiring a player like Cutler doesn't happen very often in the NFL. He has the arm strength to insure the weather will never be a factor. His backups don't have the experience to rank the team any higher than this.
Rk
Team
Points
Quarterback depth chart
17.
12.5
Matt Ryan, Chris Redman, D.J. Shockley (John Parker Wilson)
Comment: Ryan might turn into the next Tom Brady in the NFL. He can do it all but his backups have yet to prove they could ever keep things going if he gets hurt. Redman has 10 career starts, but none with distinction.

18.
12.4
Comment: Schaub is solid, but staying on his feet for a 16-game season is a big question. He's missed five games in each of the last two seasons. Orlovsky and Grossman add starting experience and probably will be asked to play sooner or later.

19.
12.3
Marc Bulger, Kyle Boller, Keith Null/Brock Berlin
Comment: Bulger had a poor season in 2008 and could struggle again with a lack of quality receivers. If the Rams protect him, he can be a top 20 quarterback. A former starter, Boller has good movement skills and provides a change of pace.

20.
12.2
Aaron Rodgers, Matt Flynn, Brian Brohm
Comment: Rodgers is better than starters for other teams above this spot, but his backups have no experience. If they had to rely on Flynn or Brohm for any long stretches during the season, the Packers would be lost.

21.
12.1
Joe Flacco, Troy Smith, John Beck
Comment: A sophomore jinx is not likely in store for Flacco, who finished with a grade of 8.0 (out of 10) as a rookie. Smith, pegged the '08 starter before an injurey handed Flacco the job, is an unknown, and Beck lacks real experience.

22.
11.9
Shaun Hill, Alex Smith, Damon Huard
Comment: Even though Hill begins the season as the starter, the battle between him and Smith is likely to go on well into the season. Neither guy is polished enough to be a top 16 quarterback and that keeps the team ranking down in the 20s.

23.
11.8
Trent Edwards, Ryan Fitzpatrick, Gibran Hamdan
Comment: Edwards is smart and has Terrell Owens, but only 11 TD passes in 2008 is a yellow flag. He also has a medical history, which means Fitzpatrick could be a factor. Fitzpatrick, however, had only eight TD passes in 372 attempts last season with the Bengals.

24.
11.7
David Garrard, Todd Bouman, Paul Smith
Comment: Garrard looks ready to return to his efficient 2007 style. He started all 16 games in 2008, despite playing behind a makeshift offensive line; another year of 40-plus sacks is possible. Bouman is 37 and would struggle if he had to play an extended time.
Rk
Team
Points
Quarterback depth chart
25.
11.6
Jason Campbell, Todd Collins, Colt Brennan
Comment: Campbell is finally in the same system for two consecutive years for the first time since high school. Collins is a veteran backup but will not come on the field unless Campbell is injured. Brennan is a fan-favorite but not ready.

26.
11.5
Kyle Orton, Chris Simms, Tom Brandstater
Comment: Orton has a lot of pressure on him as he replaces Jay Cutler. Brandon Marshall, who is always in the doghouse, can't be counted on. Simms could push Orton but for now he settles for the backup spot for a rookie head coach.

27.
11.4
JaMarcus Russell, Jeff Garcia, Charlie Frye
Comment: If the Raiders release Garcia this becomes the bottom-ranked unit. Russell has a long way to go as an NFL quarterback and the other backups offer no assurance they can move the team up and down the field if asked to.

28.
11.3
Byron Leftwich, Luke McCown, Josh Freeman, Josh Johnson
Comment: If the Buccaneers struggle with Byron Leftwich as the starter, they will turn over the quarterback reins to Luke McCown or rookie Josh Freeman, who isn't close to being ready to play. This situation could get ugly fast.

29.
11.2
Matt Cassel, Tyler Thigpen, Brodie Croyle
Comment: Cassel had a heck of a season last year, but the offensive line and receivers in K.C. are far from what he had in New England. Cassel was sacked 47 times in 2008 and that number could go up this season. Thigpen makes plays, but winning games is another matter.

30.
11.1
Derek Anderson, Brady Quinn, Brett Ratliff
Comment: Quinn will probably be first up this season but after he struggles we should see Anderson and then Ratliff. Combined, the three quarterbacks have not thrown a touchdown pass in two preseason games.

31.
10.9
Daunte Culpepper, Matthew Stafford, Drew Stanton
Comment: It is hard to evaluate the Lions' quarterback position. Culpepper has enough to play like a quarterback ranked 20th, but the team will find a way to get Stafford on the field, and he is not ready to win games just yet.

32.
10.8
Comment: Sanchez is going to be solid one day, but he will struggle to win games this year and no one else at the position has distinguished himself enough to challenge the rookie. Three QBs on a team with one experienced receiver is not good.


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