In the NFL, the fall from playoff contender to league doormat can be awful quick. One year, you have a talented team of experienced veterans. The next year, if the majority of those veterans show their age all at the same time, and you’ve made some poor drafting decisions, the team is back at square one.

That’s the situation new head coach Eric Mangini inherits as the Jets open their training camp Friday at Hofstra University. It’s easier to list the positions where the Jets don’t have questions than to list the ones where they do. But the list of the biggest issues facing the Jets this preseason starts with a very obvious number one:

Who is the starting quarterback?

Once upon a time, Chad Pennington was one of the league’s most promising young quarterbacks. But after two shoulder surgeries, it’s hard to tell if he can still compete at this level. Former Washington first-round pick Patrick Ramse y isn’t a star by any means, but he’s not as bad as his reputation. He would probably do well as a Trent Dilfer-like game manager quarterback on a team built around defense and the running game.This is not that team. On the other hand, Mangini learned from his mentor Bill Belichick that you win by eliminating weaknesses that will be obvious to your opponent. Ramse y’s game doesn’t have a hole anywhere near as big as Pennington’s inability to throw for distance.

Don’t be surprised if second-rounder Kellen Clemens is the starter by December, but while the talented Clemens may end up looking like a second-round steal, he’s not going to win many games as a rookie. If the Jets throw him into action too quickly, they risk having him pick up the bad habits that come from not being able to trust your offensive line, one reason why Houston’s David Carr has never lived up to his potential.

Brooks Bollinger goes into camp as the fourth quarterback, but since NFL teams rarely carry four quarterbacks, that’s not a really place you want to be.

Who is the starting running back?

Curtis Martin’s 2005 decline and subsequent injury was entirely predictable given his age and his large workload the prior year. He is currently penciled in as the starter for 2006, but you can’t expect a big comeback from a 33-year-old coming off knee surgery, especially one who also happens to have the third most rushing attempts in NFL history.

Derrick Blaylock was supposed to be insurance for the inevitable Martin drop-off, but he suffered his own injury after just 17 carries. 2005 sixth-rounder Cedric Houston showed flashes of talent, with good hands and an ability to finish off his runs strongly, but he’s not on anyone’s list of top young running backs. By giving him playing time this year, the Jets can figure out if Houston should be a part of the playoff contender they are trying to build, or if they need to use a high 2007 draft pick to get a starter at this position.

How young will this team go on the offensive line?

The Jets clearly believe that you construct a champion from the lines out. On draft day, they eschewed big-name players like quarterback Matt Leinart to grab two offensive linemen in the first round: left tackle D’Brickashaw Ferguson and center Nick Mangold.

Ferguson was immediately figured into the starting lineup, and Mangold will now join him because veteran center TreyTeague will miss most, if not all, of training camp with a broken left ankle. After not seeing a single snap as a rookie, 2004 fourth-round pick Adrian Jones was thrust into the lineup at left tackle last year and wasn’t very good. He’ll move over to the right side and hope to improve. In the long-term, Ferguson and Mangold are the anchors of a championship line, but in the shortterm, the quarterbacks and running backs will spend a lot of time on the ground behind the line of scrimmage.

How will the Jets fit their pieces into the new 3–4 defensive scheme?

Like his former colleagues in Foxboro, Belichick and Romeo Crennel, Mangini wants to play a 3–4 alignment. But it’s tough to switch to the 3–4 when the team can barely scrape together four solid linebackers. Jonathan Vilma is a stud in the middle — only San Diego’s Donnie Edwards was involved in a higher percentage of his team’s tackles.Victor Hobson, Eric Barton, and Brad Kassell are all adequate, but, like Vilma, will need to learn new responsibilities.

An interesting linebacker to watch is Bryan Thomas, who has never lived up to his promise as the 22nd overall selection in the 2002 draft because he couldn’t quite convert from defensive end to a standard outside linebacker. He is a definite candidate for the “elephant” role in the 3-4, the pass-rushing cross between end and linebacker made famous by former New England (now Cleveland) star Willie McGinest.

A bigger problem than the linebackers are the three players in front of them.Free agent acquisition Kimo von Oelhoffen has been an outstanding 3-4 end for the Super Bowl champion Steelers, but nose tackle Dewayne Robertson has been a bust since the Jets selected him fourth overall in 2003, and it remains to be seen if end Shawn Ellis can adapt to playing in a 3-4 scheme that requires him to occupy offensive linemen instead of pursuing the quarterback himself.If any of these players are injured, the depth behind them is quite poor.

Are there any places where the Jets don’t have questions?

Yes, special teams. Punter Ben Graham had a good first year after coming over from the Australian Football League. Kicker Mike Nugent didn’t impress anyone in his rookie year, but he certainly doesn’t have to fight for his job. With wide receivers Tim Dwight and Jerricho Cotchery, plus cornerback Justin Miller, the Jets have depth and talent in the return game.

Every other unit on the team is uncertain, although not as uncertain as the quarterback and running back positions. Cotchery is an unproven third receiver behind Laveranues Coles and Justin McCareins. Tight end Doug Jolley is still trying to recapture the promise of his 2002 rookie year in Oakland. The cornerback position features a camp battle between injury-prone free agent Andre Dyson, mediocre veteran David Barrett, and sophomore Miller, who wasn’t very impressive as a rookie. According to game charting data, Miller stopped just 24% of passes thrown in his direction, the worst figure in the league.

Mr. Schatz is editor in chief of footballoutsiders.com and author of “Pro Football Prospectus 2006.”