For all but 14 starts of the past 12 seasons, Flozell Adams protected the starting quarterback for the Dallas Cowboys, a half-dozen of them at last count. The club released him in April to avoid paying the durable 35-year-old left tackle a $2.5 million roster bonus and a 2010 base salary of $5 million.
Enter three-year veteran Doug Free, who started the final seven games at right tackle in 2009. Free has only modest experience on the left side, but he is the favorite to beat out Alex Barron, acquired from St. Louis in an offseason trade, for the right to serve as Tony Romo's new blindside bodyguard.
"Those are some really big shoes to fill," Free acknowledged.
Even if Adams played at times in 2009 as if he was operating in clodhoppers, Free does indeed step into a huge void and a daunting challenge. Perhaps because of the grandiose expectations surrounding the Cowboys -- with the team attempting not only to repeat as the NFC East champions but also to become the first franchise in league history to participate in a Super Bowl in its home stadium -- Free figures to be one of the NFL's most closely scrutinized players in training camp.
But Free, 26, won't be the only youngster under the microscope this summer. And certainly not the only young left tackle.
Ditto Brandyn Dombrowski in San Diego, where he will try to fend off veteran Tra Thomas for the right to replace standout Marcus McNeill, who also has yet to sign his restricted free agent qualifying offer.
Okung is projected to replace a potential Hall of Fame tackle, retired Walter Jones, on the left side. The Redskins were enamored enough of Williams that they will play Jammal Brown, a two-time Pro Bowl left tackle acquired from New Orleans via an offseason trade, at right tackle. Williams, a former Oklahoma standout, is projected instead as the left-side starter.
"You can't think to yourself, 'Man, I've got to be as good as the guy I'm replacing,' you know?" said New Orleans' three-year veteran Jermon Bushrod.
Last season, Bushrod replaced the then-injured Brown despite Bushrod's lack of experience (zero starts before 2009). Bushrod performed well enough for the Saints to capture a Super Bowl title.
"You've got to be patient, be yourself and understand that this is your chance," Bushrod said.
A lot of young players will get an opportunity this summer to demonstrate that they are prepared to take on the left tackle challenge. There figure to be at least eight new starters at the critical position, and that number could expand by a couple more, depending on developments in other camps. That represents a substantial turnover at a spot that not only has been crucial but also had remained pretty stable until now.
Four of the changes are because of coaches dissatisfied with the level of performance at the position in 2009.
Said Levi Brown, the Cardinals' starter at right tackle the past three seasons but poised to replace Mike Gandy (who was not re-signed) for 2010: "It's the position that every [lineman] wants to play."
The old "changing of the guard" adage still holds true, as it does at the outset of every training camp cycle.
But this could be dubbed a "changing of the tackle(s)" season.
In the past decade, the league has experienced a kind of golden age of left tackles, with premier performers such as Jonathan Ogden (Baltimore), Orlando Pace (St. Louis), Jones (Seattle) and others. But many of the tackles who will replace them are young and still must polish their games.
"I'm confident but there's still so much to learn," said Okung, who is expected to start a new era of longevity in Seattle. The Seahawks struggled to replace the injured Jones in 2009, employing four starting left tackles during the year. "You're talking about moving in for a Hall of Fame player."
The average age for projected left tackles in 2010 is 26.6 years, and the average experience is only 3.625 seasons, the lowest in at least 10 years. Nearly three-fourths of the projected left tackle starters (23 of 32) are 25 or younger. There are only five starting left tackles who are 30 or older.
"It's the one [offensive line] position everyone watches all the time," said Green Bay's Chad Clifton, the graybeard of the group (33 in September), and the only projected starter with double-digit seasons on his résumé.
Because of the unusual turnover at the position, there will be more than the usual complement of peepers on the left tackle spot for the coming season.
Len Pasquarelli, a recipient of the Pro Football Hall of Fame's McCann Award for distinguished reporting, is a senior writer for ESPN.com.