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There are a lot of elements that have contributed to the downturn in offensive production over the first six weeks of the NFL season.

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But if you're looking for one explanation right up front, then consider what has transpired, well, right up front, with offensive line units so far this season.

"It's been a little bit like a revolving door, musical chairs, roulette, whatever you want to call it," said St. Louis second-year lineman Richie Incognito, who began the year at left guard, then moved to center after a season-ending knee injury to Andy McCollum.

In six games, the Rams have used eight different offensive line starters and three starting combinations.

"Sometimes," Incognito said,"you find yourself just kind of looking, you know, from side to side, to see who's out there with you."

Given the cut-and-paste approach to which some offensive line coaches have been relegated this season, as they attempt to cobble together a workable unit from week-to-week, Incognito isn't the only lineman in the league playing with his head on a swivel. Some teams have shuffled the lines so much, it seems the starters ought to be required to introduce themselves to each other before they break the huddle for the first time.

Entering this weekend, just 13 teams have enjoyed the luxury of being able to start the same offensive line quintets in every game, and that number will be reduced by two on Sunday with the Falcons' Matt Lehr (suspension) out and the Eagles' William Thomas (questionable with a back injury) not expected to play. At the same time, primarily as a result of injury, but in some cases because of incredible ineptitude, 14 franchises already have used three or more starting line combinations.

Clearly, patchwork doesn't translate into production in the NFL. But one could make a pretty compelling case that stability on the offensive line is an integral component to success in 2006.

All-injury offensive line

You could field a pretty representative offensive line unit from among the blockers on injured reserve for the rest of the season. Here's a quintet that, when healthy, most teams wouldn't mind having: • LT Travelle Wharton, Carolina (knee): Had started 28 straight games, including 17 at left tackle, before tearing the anterior cruciate and medial collateral ligaments of his left knee in the Sept. 10 season opener. A third-round pick in the 2004 draft, Wharton played left guard as a rookie, but moved to his college position of left tackle at the outset of the 2005 season and solidified the spot. A player who was clearly improving before the injury. • LG Edwin Mulitalo, Baltimore (triceps): Powerful in-line blocker, along with tackle Jonathan Ogden, formed one of the NFL's best leftside tandems. Suffered a torn right triceps in the Oct. 1 victory over San Diego, and underwent season-ending surgery the following day. The durable, eighth-year veteran has appeared in 106 games, with 102 starts, and since 2000, had never made fewer than 14 starts in a season. • C LeCharles Bentley, Cleveland (patella tendon): Termed "the face of our free agent efforts," the former New Orleans star was rated by ESPN.com as the top unrestricted player at any position this spring. On the opening day of free agency, he signed a six-year, $36 million contract, with $12.5 million in guarantees. A two-time Pro Bowl performer, once at guard and once at center, the former Ohio State standout was to have been the cornerstone for the rebuilding of the Cleveland offensive line. In the first training camp practice, however, he tore the patella tendon in his left knee and faces a lengthy rehabilitation. • RG Damien Woody, Detroit (foot): Started the first five games of the season before a severe foot sprain forced the Lions to place him on injured reserve. A former first-round draft choice, and a Pro Bowl pick in 2003, the eighth-year veteran signed with the Lions as an unrestricted free agent in 2004, landing a deal that made him the NFL's highest-paid guard at the time. A terrific technician who uses his hands very well, he spent irst five seasons in New England, and has started in all but two of his 115 appearances. • RT Kenyatta Walker, Tampa Bay (knee): Often maligned because he has never quite lived up to his status as a first-round choice in the 2001 draft, Walker started all 16 games at right tackle for the Bucs in 2005, and has his best season. The former University of Florida star is still prone to penalties, but has developed his physical tools over the last few years. He has started in 73 of 75 appearances, and started the first three games since season, but a degenerative condition in his right knee forced him onto injured reserve Oct. 4. -- Len Pasquarelli

The 13 teams that have used the same offensive line starters through the first six weeks of this season have an aggregate 45-23 record, a .662 winning percentage. Only two of the teams, Cleveland and Washington, have losing records. Of the nine clubs that either lead their division or are tied for the lead going into this weekend, six are teams that have started the same offensive line in every game. The NFL's two undefeated franchises, Chicago and Indianapolis, are among them.

On average, teams have employed 6.4 different offensive line starters this year, or just one extra starter per club. But there are seven teams that have been forced to use eight starters, and the Carolina Panthers and Detroit Lions have used nine each. The average number of different line combinations leaguewide is 2.4, and that seems a relatively benign number, until one considers that seven franchises have used four or more different starting groups.

Offensive line coaches ought to show up for work with the pass protection diagrams under one arm and a spool of baling wire under the other.

"It's been a struggle since Day One to keep guys together," acknowledged Detroit left tackle Jeff Backus, one of only two Lions' blockers to start all six games at the same position on a line unit that has had five different starting lineups.

From a leaguewide standpoint, Backus' assertion is literally on-point, as teams began losing linemen on Day One of training camp. In the Cleveland Browns' first camp practice, center LeCharles Bentley, the centerpiece of the team's rebuilding efforts on the line, and a two-time Pro Bowl performer who signed to a six-year, $36 million contract as an unrestricted free agent, tore the patella tendon of his left knee. Offensive lines have been torn asunder since that day.

Ironically, the Browns are one of the 13 teams that have used the same starters in every game. But the loss of Bentley, a dominating player who began his career in New Orleans, forced the Browns to make seven other moves at center. And while Cleveland line coach Jeff Davidson hasn't had to break out the kind of giant eraser colleagues around the NFL have used in setting their depth charts every week, no one will convince him, general manager Phil Savage or coach Romeo Crennel that the 1-5 Browns wouldn't be far better off with Bentley in the lineup.

Said one longtime NFL offensive line coach who recently retired: "All over the league, it's some of the worst offensive line play I've ever seen. Fundamentals just seem to be shot to hell. I see guys, just from watching on television, and you can tell they're confused. You bring the most rudimentary blitz against them and it's like they've never seen it before. I'm guessing part of it is [bad] coaching, part of it is flat-out bad players, and part has to be all the injuries."

Injuries, for sure, have certainly been the overriding reason for all the offensive line shuffling. As has historically been the case for the last several years, nearly 30 percent of the players on injured reserve right now are offensive linemen. The injuries on the line have ranged from the brutal, like Bentley's patella tendon tear or the ruptured triceps of Baltimore left guard Edwin Mulitalo, to the bizarre, such as the self-imposed case of frostbite incurred by Pittsburgh right guard Kendall Simmons last week, when he feel asleep with a cooling device on the heel. At least Simmons avoided the injured reserve list.

One could assemble an impressive offensive line quintet from the players on injured reserve, a unit, in fact, that might be better than many teams' lineup.

"There's a trickle-down [effect]," said Carolina tackle Jordan Gross, forced to move from his preferred right side to the left tackle spot when the Panthers lost Travelle Wharton to a season-ending knee injury in the first game of the year. "You have to compensate. That means moving bodies around, or sliding in new guys, and things tend to get out of sync then. Whatever cohesiveness you built up in camp, it's gone. It's like you're starting all over again."

The result: A lot of sporadic, stop-and-start offenses. With, in many cases, more stops than starts.

Among the several teams for which the offensive slippage can be traced to instability on the line is the Cincinnati Bengals, a model of consistency in 2005, but racked by injuries and inconsistencies in '06.

Cincinnati used only three different starting line combinations last season and never played consecutive games without its usual five starters. But because of an early injury to center Rich Braham and now to left tackle Levi Jones, the Bengals already have deployed four different starting lineups. They'll have a fifth on Sunday, when they face Carolina, with rookie Andrew Whitworth, who has started two games at left guard, replacing Jones at left tackle. Eric Steinbach, the team's standout left guard, has started at three line positions in the first five games of the year.

The results are obvious in the Bengals' comparative statistics over the past two seasons. In the first five games of 2005, Cincinnati averaged 24.8 points, scored 15 offensive touchdowns, and ranked third in the league in total offense, and quarterback Carson Palmer had been sacked just seven times. Through five games this season, the Bengals are averaging 22.2 points and have 11 touchdowns, ranked No. 19 in the league in total offense, and Palmer has been sacked 17 times, just two fewer sacks than he absorbed in all of 2005.

Those who have seen Palmer in person suggest he might have come back too soon from January surgery to repair two torn ligaments in his left knee, and that he isn't as mobile in the pocket. But the ever-changing composition of the Cincinnati line, observers agree, also has contributed to the offensive malaise.

"We just can't get settled," said right tackle Willie Anderson, one of only two Cincinnati linemen to start every game at the same position. "It seems like it's something new every week."

In that regard, the Bengals haven't been the only team that seems to have a new starting line every week.

Arizona has used four different lineups and had three different right tackles. Carolina is also working on its third different right tackle, Jeremy Bridges, who wasn't even in camp with the Panthers. The Lions have run through three right tackles as well. Miami's sore spot, in starting four different lineups, has been at right guard, where the Dolphins have had four starters in six games. San Francisco has trotted out three different left guards and Tampa Bay has used four right guards.

There are a half-dozen teams in the league that haven't fielded the same starting lineup for more than two weeks in a row.

"Some weeks," said a veteran offensive lineman from a team whose unit has been perilously thinned by injuries, "it's almost as if they reached into a hat, pulled out some names and said, 'OK, you at left tackle, you at center,' you know? I mean, it's been that bad."

Len Pasquarelli is a senior NFL writer for ESPN.com.