Some college football jobs are safe. For instance, the only thing Texas A&M QB Johnny Manziel and Oregon QB Marcus Mariota need to fear is injury.
Other schools have no safe positions. Take Ole Miss. After a top-10 recruiting class, the Rebels are still willing to put anyone anywhere as long as it's an improvement.
College football is one of the most fluid sports in the country, and anyone can go anywhere at a moment's notice. Performances are evaluated weekly, and there are only so many positions to fill.
The following players are in the most danger of losing their jobs this spring. Some will be pressured by 2013's early arrivals. Others will be targeted by returning teammates.
Here are the 25 most precariously perched players in college football this spring.
Phillip Sims came to Virginia from Alabama with plenty of potential and high expectations. Sims did not live up to them in 2012, but he saw plenty of snaps.
Heading into the 2013 season, he will be the most experienced quarterback on the roster. Unfortunately, according to Virginia's latest spring roster, he's not the best.
It should be of little surprise to anyone that his job was in jeopardy, because it wasn't exactly secure during the season. However, if he doesn't step up before the 2013 season kicks off, his career will be over before it really started.
Right now, Sims, a junior, is No. 3 on the depth chart behind starter David Watford, a redshirt sophomore, and backup Greyson Lambert, a redshirt freshman. Sims' job is at DEFCON 1, and he had better be prepared to defend it accordingly. He's already lost a lot of ground, and it may be too late.
Demetrius Wright is already losing ground to Su'a Cravens, the superstar prospect from the 2013 class.
Wright is a good safety, has experience and is talented enough to get back on the field. But Cravens, who enrolled early, was the nation's No. 12 recruit on the 2013 ESPN 150.
It's going to be difficult for Wright to get his job back. In fact, if the quarterback situation at USC doesn't iron itself out, it wouldn't be ridiculous to see Wright move to offense as an experiment.
At this point, as long as USC is getting better, the fans will be infinitely happier with the Lane Kiffin situation.
USC quarterback Max Wittek certainly didn't do himself any favors with his subpar play in USC's loss to Georgia Tech in the Sun Bowl.
But as of March 5, Wittek is still ensconced as the starter. However, Max Browne enrolled early and will be gunning for that position until he gets it.
As far as how long that will take, well, that's all up to Wittek. The Trojans' fanbase isn't going to wait around forever for success, especially not after seeing 10 wins as recently as 2011.
Wittek has his work cut out for himself, and he can't afford to take a single week off. His job may not be as unstable as some other players on this list. But he's not on a firm foundation.
Torin Harris has already been passed on the depth chart, but it's not too late to save his cornerback job.
Much like Demetrius Wright, Harris was passed by a freshman who enrolled early. That would be Leon McQuay III, who has replaced Harris in the starting lineup.
Harris has to get his butt in gear if he wants to reclaim his position as a starting corner.
Derel Walker wasn't a headliner for the Texas A&M Aggies last season, as Ryan Swope, Mike Evans and others were standing in his way.
As the offseason claimed half of the starting wide receivers from the Aggies' squad, Walker's opportunity seemed close. Unfortunately, Ja'Quay Williams enrolled early and brought his 4-star talent to the practice field.
Experience and knowledge of the playbook can help Walker hold onto the starting spot, but Williams will not sit idly by while someone plays the game he loves in front of the fans he's waited his whole life to play for.
Walker had better be ready to put in long hours over the playbook, because that's going to be his biggest edge over Williams.
Texas had one of the nation's highest-profile mediocre defenses in 2012, and the Longhorns finished a disappointing 74th nationally in scoring defense.
Part of the problem was the linebackers' inability to make tackles. There were many instances where missed tackles plagued the Longhorns.
Demarco Cobbs wasn't the culprit for all of them, but he had more assisted tackles than solo ones. Assisted tackles aren't necessarily a bad thing. But if you saw Texas' defense last season, you know it was almost always bad if the first man to the ball couldn't bring the opponent down without help.
Cobbs is a good linebacker, but his job is not safe. Deoundrei Davis sat just outside the ESPN 150 at No. 151, and he's already at Texas looking for playing time.
If it was talent that was the issue, Davis has brought the fix. If it was coaching, then Davis' arrival won't make much of a difference.
If Cobbs wants to keep his job, he'll put in the effort to becoming a premier linebacker. If not, Davis will gladly take the spot from him.
David Ash is not finished fighting for his job. He doesn't have to worry about a spring recruit taking his job, but Case McCoy isn't going away until he graduates.
McCoy will always be the younger brother of the legendary Colt McCoy, and Mack Brown's subconscious will always be looking for signs of improvement from the youngster. Whenever Brown sees a flash of greatness from McCoy, he's going to respond quickly.
The only way Ash can combat that is by making sure that he is always better than McCoy at almost everything.
If Ash plays to his full potential (or even just 90 percent), Brown will be saying "McCoy who?" in no time. However, don't mistake Ash's presence on the depth chart at No. 1 for job security.
The comeback win against Oregon State in the Alamo Bowl was great, but it's going to take more than a win like that to solidify his position.
Quarterback Trevone Boykin is atop the TCU depth chart as we speak. He did nothing during the 2012 season except prove that he's ready to take over the Horned Frogs offense.
However, Casey Pachall is back, and he helped TCU do great things before he had to leave to get himself in order. There's a certain unwritten idea that "once the starter, always the starter" in college football.
Even Oregon State had a run-in with that unwritten rule last season, but the Beavers will be covered later in the show.
Boykin performed more than admirably in 2012 while enduring the growing pains of a rookie quarterback on the collegiate level. He gained almost a season's worth of experience while Pachall sat idle.
Yes, Pachall should be given a second chance. If he earns the starting gig over Boykin, the coaches should not hesitate to put him back in.
On the other hand, if Boykin doesn't do anything to lose the No. 1 spot, this will just have to be one of those tough life lessons for Pachall.
Whichever quarterback ends up starting, expect the Horned Frogs to contend for the Big 12 title and a berth in the Fiesta Bowl (or better if things work out perfectly).
Sean Mannion was the beneficiary of the "unwritten rule" mentioned in the previous slide. After an injury during the 2012 season, he returned for the Washington game.
He couldn't find his rhythm and tossed a few picks that cost the Beavers their perfect season. Cody Vaz stepped in after Mannion's fourth interception in that game, but it was too late.
Don't think for a minute that the coaching staff won't remember that if Mannion slips into a slump. The staff will give him time to come out of it. But if Vaz proves he's the better passer this spring, Mannion will be pulled in a heartbeat.
After all, it's all about doing what it takes to win as a team.
Clint Chelf was the second-best quarterback for Oklahoma State in 2012, but he was the go-to passer during the second half of the season.
He probably would have been the best quarterback if he'd been able to play in every game, but that's not how things worked out.
He entered the spring as the favorite to start, but J.W. Walsh will not take that lying down. For that matter, neither will Wes Lunt.
Of the two backups, Walsh is probably the bigger threat, as his touchdown-to-interception ratio was the best of the three last year.
If Chelf doesn't play his best football in spring practice and Walsh does, the Cowboys are going to have to put Chelf on the shelf this fall while Walsh wins games for them.
Adam Griffin could be the first real casualty of the Urban Meyer recruiting era. With a marquee cornerback prospect coming to town, members of the Ohio State secondary had better be on their toes.
Eli Apple was the No. 3 corner of the 2013 class and the No. 11 overall recruit. While Ohio State's Bradley Roby is probably safe, Apple is talented enough to overtake even him during the 2013 season.
Of course, Roby wouldn't get benched in that situation, Griffin would. If Griffin wants to take some advice, he should go talk to Roby about how to be a lock-down cornerback.
If Griffin doesn't watch his back, Apple will be joining Roby as the core of Ohio State's lethal secondary.
Zack Martin will face off this spring against Steve Elmer, the No. 26 offensive tackle of the 2013 class. After the lopsided loss to Alabama in the BCS Championship Game, there is little question that Notre Dame needs to beef up its line of scrimmage (both sides of it).
Of course, by facing Big Ten teams, the Irish can win plenty of games while they make their improvements. But to win a national championship, they need to first strengthen the line of scrimmage.
Martin and Elmer will engage in a heated battle for the right to start on the offensive line this spring, and Notre Dame's line will be better for it.
Regardless of which player gets the slot, the competition will make both of them better. Notre Dame may just have another 10-win season in 2013.
Again, it all starts on the line.
Devin Funchess is in for a world of hurt this spring. Michigan's offense needs all the help it can get, and Jake Butt enrolled early to attempt the rescue.
The point is that Funchess wasn't irreplaceable, and Butt will attempt to prove that he can replace him right now. If Funchess doesn't have the prowess to hold Butt at bay, his time as the starting tight end is over.
Frank Clark is on a defense that finished No. 20 nationally in scoring defense in 2012. Yes, the Wolverines' offense needs serious help, but losses to Alabama in the season opener and South Carolina in the Outback Bowl proved that Michigan's defense is also in need of serious improvement.
Taco Charlton has enrolled early to prove that he has what it takes to help the Michigan defense get to the next level. Charlton's first target on the roster will be Clark.
While there are plenty of places Charlton could eventually go, Clark's spot is the one he could occupy as a freshman. Charlton is the 116th-rated recruit in the 2013 class, and his work ethic and talent should combine to make him a starter in the fall.
That battle will be won or lost in the spring. If they are equal in talent at the end of the spring, Clark's experience will give him the starting job by fall.
Clive Walford, the starting tight end at Miami, is two inches shorter than Beau Sandland, the already enrolled recruit.
While Walford has experience and about four pounds on Sandland, he didn't have a stellar season in 2012. Of course, neither did Miami. Walford was third on the team in receiving yards with 451.
His most impressive stat was his average of 18 yards per catch. That could be enough to give him an edge over Sandland.
The biggest problem Walford faces is Sandland's 4-star status as a JUCO transfer. Having already performed well on the collegiate level, Sandland may take Walford to school this spring.
As of March 1, Walford still had his job. The spring game will tell all, though.
After the dismal season that Kansas had in 2012, the only surprise should be that the whole team didn't make this list.
Kansas is basically at rock bottom, and there's nowhere to go but up. Fortunately for the Jayhawks, Marquel Combs, the No. 2 defensive tackle from the JUCO ranks, has joined the team and figures to replace Keon Stowers in the starting lineup.
If Combs' leadership and experience take hold quickly, Kansas will begin its rise in 2013. Don't expect a lot of improvement, but definitely expect the tailspin to get under control.
Sadly, this will put Stowers on the outside looking in. But Kansas will be in a better recruiting position if it can win a few more games in 2013.
Safety Corey Moore enters spring practice with a giant target on his back. It was put there by yet another early arrival to grace this list: Tray Matthews.
Matthews will have the insanely tough task of attempting to earn a spot on an SEC depth chart as a freshman, and Moore is the man standing in his way.
Fortunately, Georgia fielded two freshmen running backs in 2012 (Todd Gurley and Keith Marshall), so Matthews knows that his task is not impossible.
As the nation's No. 129 recruit, it is an uphill battle, but it's still not a lost cause. Moore, on the other hand, needs to buckle down and make sure that an ESPN 150 recruit isn't good enough to bump him out of the starting position.
Either way, Georgia is going to contend for the SEC again, so the best player will definitely be the one on the field.
Georgia doesn't have time to mess around. This is Aaron Murray's last year.
Malcolm Mitchell and Chris Conley are both in danger of losing their starting jobs this spring. Early arrival and 4-star JUCO transfer Jonathon Rumph will be taking on the entire wide-receiver corps during practices.
Rumph is good enough to take over either one of the starters' roles, and the Bulldogs need all the help they can get to make up for the players that left for the NFL.
Mitchell and Conley should both be looking over their shoulders during spring practice, either for the ball or for Rumph. Both will be coming for them.
Giorgio Newberry has the horrible predicament of trying to replace Bjoern Werner while staving off an attack from DeMarcus Walker, the No. 40 recruit in the 2013 class who has already enrolled at Florida State.
Newberry needs to prove that he's an invaluable piece of the Seminoles' defensive line, but Walker brings a raw talent to the game that will allow him to catch up to Newberry quicker than he might think.
Florida State needs a defensive line, and however the Seminoles need to accomplish that, they will.
This spring, Mack Brown will be trying to earn the starting role that was most recently occupied by Mike Gillislee. Brown has a head start over all the incoming recruits, but there are talented running backs already enrolled at Florida.
One is Kelvin Taylor, the nation's No. 8 recruit from the 2013 class. The other is sophomore Matt Jones, who has already taken over the starting spot, according to the March 21 depth chart.
Brown has his work cut out for him. He's been passed by a sophomore, and the freshman behind him is not far behind at all. Before the spring is over, Florida may have a true freshman starting at running back.
Of course, with the Gators' passing attack as horrible as it was last season, they may opt for multiple tailbacks on the field at the same time. If that's the case, Brown only needs to be better than one of the other two.
Defensive end Corey Crawford's position as a starter is in question this spring.
JUCO transfer Shaq Lawson is already at Clemson, and he is surely making a run for a starting position on the defensive line. The addition of just a couple more talented players on defense last season could have had Clemson playing in the national championship game, as the Tigers fell to Florida State by 12 points and to South Carolina by 10 in the regular season.
Fortunately for Clemson, Lawson is enrolled. That's not good news for Crawford, though, as his position on the depth chart is now in question. If anyone's taking Lawson's spot, it's the JUCO transfer. Other than that, he should be safe.
Kiehl Frazier did not have the greatest performance in 2012, but neither did the Auburn Tigers as a team. Frazier is talented enough to keep the starting job, but last season put him on the same level as the rest of the quarterbacks on the roster.
Frazier is going to be a part of one of the most heated quarterback battles in the country this spring. Both Clint Moseley and Jonathan Wallace will be targeting him.
Frazier may have been the favored starter in 2012, but with Auburn's need to revamp the entire team, he may be more useful somewhere else.
Auburn is hoping for a new era starting in 2013. Frazier may or may not be the leader in that new era, but he has all spring to prove that he is worthy. If not, someone else will take the lead from him.
T.J. Yeldon may be the least worried person on this list, but he is facing the roughest competition. Not only will top-10 running backs be coming in the fall, there's already a 243-pound one enrolled in Tuscaloosa.
His name is Derrick Henry, and he is the No. 9 recruit of the 2013 class. He's also the No. 2 running back.
Yeldon is firmly established as the go-to running back, so the worst he will become is the second-in-command. However, if anyone can break Yeldon's grip on the lead role, it's the record-breaking Henry.
Don't look for Yeldon to lose this battle, but don't overlook it, either.
Tight end Brian Vogler is in danger of losing his starting role to Malcolm Faciane. But both are in danger of being passed by freshman O.J. Howard.
Howard is the No. 45 recruit of the 2013 class, and he's already at the Capstone. Vogler is the most endangered starter simply because he has more people gunning for his job than the other starting tight end, Jalston Fowler.
The competition for the starting job will be fierce this spring.