Florida and Ohio State played for the national championship at the end of last season, but each enters the 2007 campaign with more question marks than the Riddler.
The Gators, who beat the Buckeyes 41-14 to win their second national title in football, must replace nine starters on defense, including All-American safety Reggie Nelson and the entire linebacker corps.
The Buckeyes lost nearly as much talent on offense, including Heisman Trophy winner Troy Smith, receivers Ted Ginn Jr. and Anthony Gonzalez, and leading rusher Antonio Pittman.
"I've got the same questions as everyone else," Ohio State coach Jim Tressel said. "Who's going to be the quarterback? Who's going to catch the balls? Who's going to be the leading ground gainer?"
A look at other teams that have big shoes to fill this season:
The Broncos must replace quarterback Jared Zabransky, who was 35-5 as a starter, including an improbable 13-0 in 2006. Junior Bush Hamdan and senior Taylor Tharp will battle for the starting job during preseason camp. One must emerge as a consistent passer for junior Ian Johnson to match his '06 production.
The Bears had one of the country's most explosive offenses in 2006 with the three-headed monster of quarterback Nate Longshore, receiver DeSean Jackson and tailback Marshawn Lynch. But Lynch entered the NFL draft after running for 1,356 yards and 11 touchdowns as a junior. Senior Justin Forsett, who played behind Lynch the last three years, might be poised for a breakthrough season. He averaged better than six yards per carry and makes up for his lack of size with great speed and toughness.
If the Tigers are going to contend for the ACC's Atlantic Division title, they'll have to replace defensive end Gaines Adams, the league's Defensive Player of the Year in 2006. Adams produced as many big plays as any player in the country last season, with 12½ sacks, 16½ tackles for loss, three fumble recoveries, two forced fumbles and six pass breakups. Junior Phillip Merling had 39 tackles and seven tackles for loss playing opposite Adams last season, but he'll command more attention now that Adams is gone. Senior Kwam Williams and sophomore Ricky Sapp are battling to replace Adams at the other end.
The Gators must replace three starters in the secondary, and it's impossible to replace a player like Reggie Nelson. The All-American safety did everything during Florida's national championship season: He was sixth on the team with 51 tackles, second with six interceptions, recovered a fumble and blocked two kicks. With Nelson as its leader, the Florida secondary did not allow a passing touchdown in seven of 14 games last season. Nelson and cornerback Ryan Smith combined for 14 interceptions, most by any duo in the country.
The Gators are working junior Markus Manson and sophomore Markihe Anderson at cornerback in preseason camp, with sophomore Wondy Pierre-Louis and freshman Joe Haden also figuring to get in the mix.
The Yellow Jackets went to Calvin Johnson so much during the past two seasons that they were accused of relying on their star receiver too much. In 2006, Johnson caught 76 passes for 1,202 yards and 15 touchdowns; in the '07 NFL draft, the Detroit Lions selected him No. 2 overall. Because of his rare combination of size and speed, Johnson made opponents change the way they defended the Yellow Jackets.
"It wasn't relying on Calvin Johnson," Georgia Tech coach Chan Gailey said. "It was trying to get the ball to one of the best players in the country. There is a difference between relying on a player and trying to get the ball to a great player."
The Yellow Jackets will try to replace Johnson with a combination of players, including junior James Johnson, who caught 39 passes for 608 yards and seven touchdowns in '06. Senior Greg Smith must step up after catching seven passes for 113 yards and two touchdowns last season. Redshirt freshman Demaryius Thomas (6-3, 220) is the player the Yellow Jackets are most excited about.
"If you add us up together, we can do what Calvin did," Thomas said. "We've got to step it up."
Replacing JaMarcus Russell, the No. 1 pick in the NFL draft, won't be an easy task for the Tigers. At least coach Les Miles can plug in senior Matt Flynn, who has some game experience. Flynn started in place of the injured Russell in the 2005 Peach Bowl against Miami and was named offensive MVP after throwing for 196 yards and two touchdowns in a 40-3 victory. Highly regarded sophomore Ryan Perrilloux, who was suspended from the team for much of the offseason, was reinstated before preseason camp opened.
The Wolverines lost a boatload of talent on defense, including All-American cornerback Leon Hall. End Rondell Biggs is gone, too. But replacing space-eating tackle Alan Branch and pass-rushing end LaMarr Woodley are of utmost concern. Junior tackle Terrance Taylor is the lone returning defensive lineman for coordinator Ron English's unit. Junior end Tim Jamison had 4½ sacks in 2006, and sophomore Brandon Graham showed much improvement during the spring. Junior Will Johnson figures to move into the tackle spot vacated by Branch.
While former Fighting Irish quarterback Brady Quinn slipped to No. 22 in the NFL draft, he was invaluable in South Bend. Quinn broke 36 school records during his three seasons as a starter and won 29 games, tied for most in school history.
Notre Dame entered preseason camp with three quarterbacks contending for the starting job, each of whom has no experience in college. Junior Evan Sharpley was Quinn's backup in 2006 but threw only two passes. Sophomore Demetrius Jones is the most athletic and mobile, and freshman Jimmy Clausen was the No. 1 quarterback recruit in the country before enrolling at Notre Dame in January.
Whether the Buckeyes can replace Heisman Trophy-winning QB Troy Smith and speedy receivers Ted Ginn Jr. and Anthony Gonzalez likely will determine if they can challenge Michigan, Penn State or Wisconsin in the Big 10 championship race.
While leading Ohio State to the Big 10 title and a spot in the BCS championship game last season, Smith threw for 2,542 yards with 30 touchdowns and only six interceptions. Junior Todd Boeckman, Smith's possible replacement, left spring practice in a three-way battle with Rob Schoenhoft and Antonio Henton for the starting job. Boeckman, 23, has been waiting patiently behind Smith for two seasons; Boeckman delayed his enrollment at Ohio State one year as a grayshirt (delayed enrollment) and then redshirted in 2004. Schoenhoft, a sophomore, threw the only touchdown in the spring game.
"Somebody is going to emerge as the quarterback," Tressel said.
Ginn and Gonzalez, each of whom was selected in the first round of the NFL draft after leaving Ohio State as juniors, might be more difficult to replace than Smith. Ginn was an explosive receiver and kick returner and perhaps the fastest player in college football. Gonzalez had underrated speed and sure hands. They combined to catch 110 passes for 1,515 yards and 17 touchdowns in 2006.
Junior Brian Robiskie emerged as a solid No. 3 receiver last season, catching 29 passes for 383 yards with five touchdowns. Sophomore Brian Hartline must jump from No. 4 receiver to No. 2 this season. The Buckeyes believe sophomore Ray Small, who played at the same high school as Ginn, has game-changing speed like his predecessor.
Heisman Trophy candidate Ray Rice emerged as the Scarlet Knights' most explosive player last season, running for 1,794 yards, second-most in Division I-A. But the tough-nosed runner might not be as productive without departed fullback Brian Leonard, an underrated blocker and runner, who was as much a part of Rutgers' unexpected success as anyone. Rice has to replace Leonard as a tough blocker to protect quarterback Mike Teel, and sophomore Kordell Young must become a more complete player to ease Rice's workload.
Gamecocks coach Steve Spurrier lost the most important piece of his Cock 'N' Fire offense when receiver Sidney Rice departed after only two seasons at South Carolina for the NFL. Rice caught 142 passes for 2,233 yards and 23 touchdowns the past two seasons combined. Junior Kenny McKinley is a bona fide No. 1 receiver (51 receptions in 2006). Several newcomers -- Chris Culliver, Jason Barnes, Joe Hills and Dion Lecorn -- must emerge for Spurrier's pass offense to be truly effective.
Tennessee's trio of receivers -- Robert Meachem, Jason Swain and Bret Smith -- combined to catch 159 passes for 2,439 yards and 22 touchdowns in 2006, helping quarterback Erik Ainge resurrect his career under offensive coordinator David Cutcliffe. The departed players combined for 60 percent of the team's receptions, 71 percent of its receiving yards and 92 percent of its touchdown catches (only two other players caught a touchdown last season).
The Volunteers will turn to several unproven players and newcomers to replace the trio. Juco transfer Kenny O'Neal, a former Florida State player, and prep school product Brent Vinson might be the most prepared to help because of their speed. Junior Lucas Taylor, a former quarterback, caught 14 passes and threw a touchdown last season. Sophomore Quintin Hancock has good size, while sophomore Austin Rogers is coming off an injury-filled season.
The Longhorns must replace All-America defensive backs Michael Griffin and Aaron Ross, each of whom was selected in the first 20 picks of the NFL draft. Ross, who had 57 tackles, six interceptions and 19 pass breakups last season, won the Thorpe Award as college football's best defensive back. Griffin, a hard-hitting safety, led the Longhorns with 88 tackles and had four interceptions.
Texas also must replace departed cornerback Tarell Brown, who started 35 games during his career. Returning starter Marcus Griffin and converted linebacker Drew Kelson should be steady at safety, but several players are competing for the cornerback jobs. Ishie Oduegwu and Deon Beasley are perhaps the most talented, but each is inexperienced.
The departed receiver duo of Dwayne Jarrett and Steve Smith combined to catch 141 passes for 2,098 yards and 21 touchdowns in 2006. While neither receiver had blazing speed, each supplied quarterback John David Booty with crisp routes and solid hands. Junior Patrick Turner moves to No. 1 receiver after catching 29 passes for 272 yards and two touchdowns. Sophomores Travon Patterson and Vidal Hazelton and redshirt freshmen Jamere Holland and David Ausberry are faster receivers who might become big-play weapons.
The Badgers return four starting offensive linemen, but replacing Joe Thomas, the No. 3 pick in the NFL draft by the Cleveland Browns, is a tall order. Sophomore Jake Bscherer and redshirt freshman Gabe Carimi (6-8, 292) were battling for the position during preseason camp, but senior Danny Kaye joined the competition during preseason camp. Carimi missed a month of work during the offseason because of appendicitis. If one of them can protect the quarterback, the Badgers will be in the thick of the Big 10 title race.
Mark Schlabach covers college football and men's college basketball for ESPN.com. You can contact him at email@example.com.