It's been said over and over by sports analysts across the nation: any good team needs a good quarterback to compete.
Of course, this golden rule has been broken a few times: who quarterbacked the 1985 Chicago Bears? The 2000 Baltimore Ravens? The 2002 Tampa Bay Buccaneers?
Jim McMahon, Trent Dilfer, and Brad Johnson, for anyone keeping track.
But those guys would have been no more than a back-up on most other teams in the league those years. They didn't win games, but they didn't lose them either.
On the other hand, some teams have a logjam of talent at the quarterback position, and could field a viable option for a second quarterback should their starter go down.
Here are some of the back-ups who look like viable starters in the NFL.
Although Bulger was able to continually to produce from 2002 to 2006, his play ultimately suffered for the Rams' failure to surround him with any talent, except, of course, Steven Jackson.
He still has what it takes to start, but Bulger landed in a good spot in Baltimore. He won't be asked to do a whole lot in the rush-heavy Ravens offense.
He has to eliminate the possession problems, though, such as turnovers and incompletions, but still has the moxie to lead a team like the Ravens.
Although our most recent memory of Collins is the first half of a 59-0 drubbing at the hands of the New England Patriots on the tail end of Tennessee's 0-6 start, this is the same quarterback who led a team with fewer weapons on offense to a 10-0 start in 2008.
Having Chris Johnson helps both in taking the pressure off and opening up play action, but Collins' veteran discipline made him a dangerous quarterback in the '08 season even simply as a game manager.
Despite a down year in 2009, the cagey vet can still get it done in the NFL.
Even when surrounded by a less-than-stellar cast of characters in Seattle, Wallace put up impressive numbers with 11 touchdowns and only three interceptions.
The team consistently put up between 17 and 23 points, but the defense simply couldn't match that output.
It's clear that the Browns are looking to play a ball control style of offense, which plays perfectly to Wallace's style of quarterbacking.
Jack Delhomme looks like the short-term answer at quarterback, and it doesn't appear Wallace will get a crack at the starting job.
If Delhomme should go down, though, Wallace makes a great replacement.
He has one irreplaceable characteristic that sets him apart from other back-up quarterbacks: Starting experience in the NFL. He went 6-4 as a starter in Houston in downtime for Matt Schaub.
He looked as sharp as ever in preseason action, and had quelled the nerves of fans who were concerned about the Vikings' quarterback situation sans Brett Favre.
Not only that, but he's the consummate team player. Rosenfels, the only one whose position on the depth chart was affected, was among the guys in the Vikings' locker room who were hoping Favre to come back.
"The Big Gradkowski" looked like a sure thing at quarterback until Oakland picked up Jason Campbell.
He may have only gone 2-2 as a starter for the Raiders, but he looked a heck of a lot better than JaMarcus Russell (though that isn't saying much).
The sample size may be too small on Gradkowski to make a judgment call one way or the other, but the simple fact that he was able to pump a sense of optimism into a listless Oakland Raiders offense is nothing short of miraculous, and is a testament to his leadership abilities.
It's not like the Raiders have an awful lot invested in Campbell; they only gave up a fourth-round pick for him.
With Campbell injured in the preseason, Gradkowski may be good enough to hang onto the starting job even when Campbell returns in 2010.
Injury concerns aside, Chad Pennington has proven himself to be a viable starter in the NFL. He moved the hyphen for the Dolphins in 2008, who finished 11-5 after going 1-15 just the season prior.
Pennington is the consummate game manager. He's not the big-arm quarterback that Jets fans salivate over (perhaps that was why he was shown the door), but he doesn't turn the ball over.
If he can stay healthy, he makes a great option for teams in need of answers at quarterback.