Does the NFL have an O-line crisis?

Comparisons are the best part of a training camp tour.

I go from camp to camp with the chance of putting rosters in perspective. I remember last year visiting several of the top AFC teams and thinking some weren't as good as they had been the previous season. When I visited some of the lower-echelon AFC teams, I believed the conference was down. The AFC went 25-39 against the NFC, but the Baltimore Ravens won the Super Bowl.

Midway through this year's 12-team tour, I started wondering about the depth on offensive lines.

As I stand along the side watching practice while peeking at depth charts, I start the mental exercise of trying to figure out the three or four top backup offensive linemen. At too many stops, I struggled to come up with more than one or two good backups.

As we watch players go down with injuries at accelerated rates, major holes are already appearing among the blockers. Start with the Denver Broncos and their problems at center. J.D. Walton was supposed to be the starter, but he's expected to miss at least the first half of the season as he recovers from a second surgery on his left ankle. The Broncos brought back Dan Koppen, but he blew out an ACL in late July, ending his season. Team executive vice president John Elway talked Ryan Lilja out of retirement, after Lilja had offseason toe and knee surgery.

In Cleveland, I tried to figure out the backups, and now I'm at a complete loss. The Browns had a nice left guard competition between Shawn Lauvao and Jason Pinkston. That's unraveled. Lauvao needed knee surgery that could cost him regular-season games. Pinkston suffered a high-ankle sprain Thursday night. The Browns could enter the season with a third-string guard starting.

The Atlanta Falcons knew things could be thin along their offensive line. Cap economics forced them to release right tackle Tyson Clabo, who was not affordable at $5.5 million a year. They believed they could get by with 2012 third-round pick Lamar Holmes and Mike Johnson. Johnson broke an ankle during a dual practice against the Cincinnati Bengals, and Holmes is raw and has been struggling so far.

Stability and durability on the offensive lines might be determining factors in 2013. The Philadelphia Eagles crumbled last year in part because their offensive line broke down. Left tackle Jason Peters didn't play a game, and only one starter, guard Evan Mathis, made it through 16 games.

Things were even worse in Tennessee. Coach Mike Munchak, a Hall of Fame blocker, started a league-high 11 different blockers in 16 games, digging into their depth for six backups. Jacksonville and Buffalo started 10.

If there are only one or two strong backups on most rosters, you can understand the impact of injuries along the offensive lines. A broken line could lead to an injured quarterback. It doesn't take long for a few injuries to lead to a shattered season. General managers say most rosters are lucky to have five solid starters and one or two decent backups.

The problem goes beyond just the $123 million salary cap. Although it can be blamed for the lack of depth at many positions, it can't be completely faulted for the offensive line woes.

This may be why the NFL needs to go to a developmental league. Right now, drafted blockers sign four-year contracts, but if they aren't playing by their third or fourth seasons, they get cut, bounce around the league and slip through the cracks. Look at the numbers. San Francisco, Minnesota and the New York Jets were the only teams who had five starters survive 16 starts. The 49ers and Vikings made the playoffs and are considered to have two of the best offensive lines in the league.

The average team, though, used 7.53 different starters last season. Coaches and general managers must figure out whether they have one or two solid backups. The numbers indicate the average team will have to go three-deep into backups to make it through a 16-game marathon.

This week's rash of offensive line injuries makes me wonder if line injuries will be more of a problem this year. The Oakland Raiders lost left tackle Jared Veldheer for three months because of triceps surgery. The Green Bay Packers lost left tackle Bryan Bulaga for the season with a torn ACL and have to go with a fourth-round rookie, David Bakhtiari. Right tackle Rodger Saffold is banged up again in St. Louis. Houston Texans guard Wade Smith needed minor knee surgery.

Survival along the offensive line could be the key to the 2013 season.