There's a common saying that NFL stands for "not for long," and in many ways that's very true.
As the Alex Smith situation in San Francisco clearly showed last year, for most players, their grip on a spot in the starting lineup is constantly tenuous, even if they've played fairly well.
If those players have struggled, their grip is just that much looser.
Add in the annual player carousel that is free agency and the NFL draft, and many 2013 starters may well have lost that grip altogether, including those listed here.
The Cleveland Browns drafted quarterback Brandon Weeden last year with the second of their two first-round draft picks in the hopes that he would be the franchise's quarterback of the future.
At this point, unless the 29-year-old's play improves, Weeden may not even be the quarterback of the present.
The Browns recently signed veteran free agent Jason Campbell, and while Terry Pluto of The Cleveland Plain Dealer reports that Weeden will take the majority of first-team reps this offseason, the arrival of Campbell means that Weeden's proverbial leash just got a heck of a lot shorter.
Speaking of short leashes...
After two seasons and a 5-19 record as the starting quarterback for the Jacksonville Jaguars, there's no assurances that Blaine Gabbert will be the starter again in 2013.
As Ryan O'Halloran of The Florida Times-Union reports, the Jaguars are fully expected to bring in competition for Gabbert this year after a pair of very uneven seasons in the NFL.
For his part Gabbert, who threw for 1,662 yards and nine touchdowns in 10 games in 2012, welcomes that competition, telling O'Halloran, “The best guy is going to win. It's going to be a blast."
There are short leashes, there are really short leashes and then there's Mark Sanchez of the New York Jets.
After a nightmarish 2012 season that saw Sanchez turn over the ball 26 times and get benched, the NFL future of the fifth-year pro is very much at a crossroads.
According to Jim Corbett of USA Today, head coach Rex Ryan has indicated that Sanchez will get the first snap under center when training camp opens, but the starting job for Gang Green is open to competition.
The addition of David Garrard only muddies the waters further in that regard, but Sanchez is trying his best to maintain his tenuous grip on the gig, working out with former pro Jeff Garcia in an effort to get a leg up on the West Coast offense that new offensive coordinator Marty Mornhinweg is installing in New York.
Bernard Pollard was the starting strong safety for the Super Bowl champion Baltimore Ravens in 2012.
George Wilson was a 16-game starter for the Buffalo Bills a season ago. He topped 100 tackles and ranked among the top 10 players at his position according to Pro Football Focus.
In 2013, one of these veterans is going to be out of luck and coming off the bench.
The Tennessee Titans signed first Wilson and then Pollard in free agency, and with Michael Griffin penciled in at free safety, the stage is set for a good old-fashioned training camp battle between Pollard and Wilson at the back end of the Tennessee secondary.
If you want to see just how fickle fate can be in the NFL, you need look no farther than Jacksonville Jaguars defensive end Jeremy Mincey.
Two years ago, the 29-year-old Mincey racked up career highs in both tackles (57) and sacks (eight), and the team rewarded him with a four-year, $20 million contract.
Last year, the bottom fell out, with Mincey tallying only three sacks and ranking outside the top 40 players at his position according to Pro Football Focus.
Now, with Jason Babin set to play the "Leo" position in new head coach Gus Bradley's defense, and the Jaguars considering taking a defensive end with the second overall pick according to Vito Stellino of The Florida Times-Union, Mincey may find himself out of the starting lineup altogether.
Sometimes young players in the NFL are thrown into the fire before they're ready, and such was the case in 2012 with Arizona Cardinals offensive tackle Bobby Massie.
The then-rookie was drafted by the Redbirds with the hopes that he would be their right tackle of the future, but injuries forced Massie into a prominent role before he was ready.
The result was a disaster, with Massie allowing an eye-popping 13 sacks, most in the NFL.
Granted, his play improved as the season wore on, but if the Cardinals complete their trade with the Oakland Raiders for quarterback Carson Palmer, then an offensive lineman becomes the leading candidate for the seventh overall pick.
Whether that player starts on the right side or kicks Levi Brown to right tackle, one thing is certain.
You do not want Carson Palmer, who is about as nimble as a lamppost, protected by a turnstile.
The Indianapolis Colts were a surprise playoff team in 2012, but one of the bigger surprises within the surprise was that Pat Angerer, who led the team in tackles in 2011, had absolutely nothing to do with that.
Granted, a broken foot got Angerer's season off on the wrong, um, foot, but even once he was reportedly healthy, Angerer found himself watching as a platoon of Kavell Conner and Moises Fokou played inside linebacker next to Jerrell Freeman for the Colts.
Now, however, Angerer has had an entire offseason to get healthy and Fokou is in Tennessee, so Conner will likely have a battle on his hands in training camp if he wants to stay a starter.
Not only is A.J. Hawk of the Green Bay Packers in danger of losing his starting spot, but there's a good chance he could lose his roster spot as well.
Yes, the eighth-year pro is coming off a career-high 120 tackles, ranked in the top 20 among inside linebackers last year according to Pro Football Focus, and just agreed to lower his salary cap figure in March.
However, as Tom Silverstein of The Milwaukee Journal-Sentinel reported at the time, Hawk's redone deal was a straight pay cut, not a restructuring.
Add in that the Packers just re-upped Brad Jones, have promising youngster Terrell Manning waiting in the wings and have both Desmond Bishop and D.J. Smith returning from injury, and if the latter pair can show they're healthy the Packers may just decide to cut Hawk's salary some more.
Like all the way down to zero.