The NFL is a league of constant change. Only a select few players have any kind of job security; everyone else is fighting to keep his job every single year.
As an influx of young talent bursts onto the scene, older veterans must prove that they are still effective and worth paying a little extra to have around.
However, teams are always looking to get younger, and the faster you can insert younger players into the starting lineup, the faster they can develop.
Here's the best rookie vs. veteran battle on every roster.
After failing to retain Ben Grubbs in free agency, the Ravens will have to rely on competition to determine who will be the new starting left guard.
So far, Kelechi Osemele is getting plenty of first-team reps in OTAs. Jah Reid also took repetitions with the first team.
While we will learn more about where these two stand in training camp, right now, I would consider Osemele to be the favorite to take over. Osemele has more raw talent than Reid, and his upside is more enticing.
This battle may come down to whether or not Osemele can pick up the offense fast enough for the coaching staff to trust him not to blow assignments and protections.
Predicted Winner: Kelechi Osemele
The Steelers have been juggling the offensive tackle spot for several years now, but after spending a second-round pick on Mike Adams, it seems like they want to solve the position battle once and for all.
Adams is a very athletic player who's much better in pass protection than he is in the run game, but at left tackle, I would prefer a pass-blocking specialist over a run-blocker.
Jonathan Scott saw some playing time last year, but was absolutely abused in a game against the Colts and does not appear to be legitimate starting material at this point.
If for some reason neither player takes the reins and convinces the coaches that he could start, a likely scenario is Marcus Gilbert, the team's right tackle, making a move over to the left side.
Still, as of right now, it looks like it's Mike Adams' spot to lose.
Predicted Winner: Mike Adams
The Bengals added a small army of veteran cornerbacks to add competition, such as Terence Newman and Jason Allen, but the real competition will be between the incumbent Nate Clements and the team's top draft selection, Dre Kirkpatrick.
There's a chance that Leon Hall may not be ready to go by the start of the season. If that's the case, it's a virtual certainty that Kirkpatrick and Clements would be the opening-day starters.
However, once Hall comes back, the team will have to decide whether it wants to play the rookie or the savvy veteran.
While much of the decision will be based on results from training camp, as of right now, it makes more sense to place Kirkpatrick, a terrific tackling and instinctive corner, in the slot, while Clements mans the outside opposite Hall.
Predicted Winner: Nate Clements
This is one of the most intriguing battles in the NFL. While the Browns want Brandon Weeden to start (otherwise, they wouldn't have spent a first-round pick on him), Colt McCoy is taking the first-team reps in OTAs.
However, even though McCoy is enjoying being able to work with the first team right now, it will probably not last long, according to Marty Gitlin of CBS Sports. Weeden's passes are apparently much more "crisp" in comparison to McCoy's "wobbly" tosses.
McCoy is probably working with the first team in OTAs simply because he knows the offense better—or perhaps the coaching staff is sending Weeden a message, saying that they want him to earn the job outright.
In any case, I expect Weeden to be the Browns' starter by opening day.
Predicted Winner: Brandon Weeden
While Chris Cook and Antoine Winfield are the likely two starting corners in Minnesota, the slot corner position is up for grabs.
Josh Robinson is the current favorite to win the job; the third-round pick has great speed (4.29 40-yard dash at the combine) and ball skills. If he's impressive enough in camp, he may even push Chris Cook to start on the outside.
However, Chris Carr is an ideal fit as a slot cornerback. He's a sure tackler and a physical player, which is exactly what you want in a slot corner.
Carr is more experienced and will likely win the job, but I expect Robinson to get some playing time in some way.
Predicted Winner: Chris Carr
While Israel Idonije is very good against the run, he had just five sacks in all of 2012 despite playing opposite Julius Peppers.
The Bears know how good their pass-rush would be if they could get some kind of threat opposite Peppers and thus chose Shea McClellin to be that man.
Not only is McClellin a better pass-rusher, he's also adept in coverage and will allow the Bears to be more creative with what they do up front.
However, Shea is a bit undersized to be a base 4-3 end and could be a bit of a liability against the run. Still, even if he fails to usurp Idonije's starting job, he will see plenty of time in obvious passing situations.
Predicted Winner: Shea McClellin
The Packers clearly missed Cullen Jenkins last year, as evidenced by how fast they went from being one of the top pass defenses in the league to the worst in 2011.
Jerel Worthy, a second-round pick out of Michigan State, is expected to fill that role, but he will have to beat out C.J. Wilson before he's handed that starting job while Anthony Hargrove serves his eight-game suspension from Bountygate.
Even though Worthy is a rookie, he's still immensely more talented than Wilson. Unless he struggles mightily with the new playbook or appears to be a total bust, I expect Worthy to be the opening-day starter opposite Ryan Pickett.
Predicted Winner: Jerel Worthy
So far, Riley Reiff appears to be as every bit as good as the Lions hoped he would be and is already taking reps at left tackle.
Eventually, Reiff will take over the starting job at either left or right tackle. The only questions that remain are what position he will take and when he will take it.
In the short term, Reiff could easily beat out Gosder Cherilus at the right tackle spot, but I would not be surprised if he outplays Jeff Backus in training camp for the left tackle spot. If he goes to right tackle, it will likely only be a temporary move before he takes over on the left side.
Where Reiff plays this year will depend on the comfort level of the coaching staff in having a rookie protect the blind side of their often-injured quarterback.
Predicted Winner: Riley Reiff
The Patriots raised a lot of eyebrows when they moved up in the draft to select Dont'a Hightower. While he brings a lot of ability to the table, the Patriots already have two inside linebackers, Jerod Mayo and Brandon Spikes.
It remains to be seen whether or not the Patriots go with a 4-3 or a 3-4 defense next year. What direction they go in will determine who will play at what linebacker spots.
If the Patriots stay in a 3-4, Hightower will battle Spikes for the starting inside linebacker spot opposite Mayo. I would give Hightower the advantage here because of his versatility and ability to play on all three downs.
If Bill Belichick elects to go to a 4-3, I would say that there is a very good chance that Hightower moves to an outside linebacker position and plays a Mike Vrabel-type role. What Belichick does with his other linebackers remains to be seen.
Predicted Winner: Dont'a Hightower
Now that Reggie Bush has now cemented himself as the starter, the Dolphins will need to determine who his backup will be. Because Bush is not a 25-carry-a-game kind of back, finding a competent backup is crucial.
Daniel Thomas was a bit underwhelming and struggled to stay healthy last season. The Dolphins drafted Lamar Miller out of Miami in the fourth round simply because he presented too much value to pass up.
While the Dolphins probably did not have any intentions to come away from the draft with a competition at the backup running back spot, they now have one on their hands.
While Thomas is a bigger back who can probably handle a bigger workload, Miller has much more speed and ability in space than Thomas and has an excellent chance to win the job in training camp.
Predicted Winner: Lamar Miller
The Jets drafted Demario Davis in the third round to be an eventual replacement for Bart Scott. Scott, however, will spend at least one more season with the team, leaving Davis duties on special teams and as a nickel linebacker.
That is, of course, assuming he beats out Josh Mauga, who filled in for Scott in a variety of packages last year.
Davis is much more athletic and has more upside than Mauga, but Rex Ryan tends to be hesitant when it comes to inserting rookies into his defense. Davis will have to win the backup ILB job outright if he wants to see the field on the regular defense.
Predicted Winner: Demario Davis
Now that Demetress Bell is an Eagle, the Bills will have to find a new left tackle from within.
Chris Hairston, who looked decent in a few starts last year, has been given the vote of confidence from GM Buddy Nix.
However, Nix knows that he cannot just hand the job to Hairston without some competition. The Bills picked Glenn in the second round to provide that competition.
Glenn is probably more suited to play guard than tackle, but he's a versatile and athletic player that will make a run at Hairston's job. However, the Bills will only give Glenn the job if he blatantly outperforms Hairston, which seems a bit unlikely.
Predicted Winner: Chris Hairston
Once Hakeem Nicks comes back from his injury, it will be interesting to see who takes over the slot position.
So far, Rueben Randle is causing a lot of buzz around the organization after an impressive mini-camp. Ramses Barden, on the other hand, is a talented player in his own right who has struggled with injuries.
While Randle may be more talented, Barden has more experience. This competition will come down to whether or not Randle can pick up the offense in time so the coaches trust him on the field.
Predicted Winner: Rueben Randle
The Eagles clearly struggled to find a competent slot corner last season.
Joselio Hanson is more experienced than Brandon Boykin, but Boykin has elite speed and a lot of upside that would be enticing.
Still, after what the Eagles went through last year in trying to find an adequate slot corner, I would be surprised if they handed the keys over to the rookie.
Predicted Winner: Joselio Hanson
The Redskins caused quite a stir after drafting Kirk Cousins on the same weekend they took Robert Griffin III, but they would not have taken Cousins if they did not think he could play.
Rex Grossman, for all of his faults, is still a serviceable quarterback who can at least get you through a game or two in case of an injury.
If Kirk Cousins is everything the Redskins think he is, he should be able to put up a good fight for the backup quarterback job.
Predicted Winner: Rex Grossman
There's a lot of uncertainty surrounding the Cowboys slot receiver position now that Laurent Robinson is in Jacksonville.
Kevin Ogletree is penciled in as the starter, but he will face fierce competition from a number of players, Danny Coale among them.
The Virginia Tech product has a lot of short-area quickness and burst, making him an ideal slot receiver, but he will have to learn the system quickly in order to be able to compete.
Predicted Winner: Kevin Ogletree
The Jaguars need to find themselves a consistent starter opposite Jeremy Mincey. Aaron Kampman was brought in to be that guy, but he has struggled to stay healthy.
Branch is an explosive athlete who will certainly challenge an aging Kampman for the job. If Kampman cannot retain his job, there's a decent chance that the Jaguars would rather cut ties with the aging veteran than keep having to deal with his injuries.
Predicted Winner: Andre Branch
As the Colts make the transition to a 3-4, they will need a nose tackle.
Antonio Johnson was supposed to be that player coming into the offseason, but Josh Chapman stands a very good chance of at least taking significant playing time away from him.
Chapman, the nose tackle in the great Alabama defense, is an ideal two-gap player who will fit perfectly into what the Colts want to do on defense. If he does not win the job this year, it should be his sooner than later.
Predicted Winner: Josh Chapman
Mike Martin is not an overly athletic player, but he's an extremely powerful man and an incredibly hard worker who will set the tone.
One of the captains of the team at Michigan, he will compete as hard as possible for the starting job with Karl Klug, a fifth-round pick from the 2011 draft.
Martin was drafted higher and has more potential as a one-technique defensive tackle. It would not surprise me at all to see him win the starting job as a rookie.
Predicted Winner: Mike Martin
In a rather curious move, the Texans decided to use their first-round pick on an outside linebacker despite getting great production from Connor Barwin and Brooks Reed last year.
While Barwin is cemented as the starter, Reed is a bit of a wild card, as he sometimes runs himself out of plays and is a bit undisciplined.
The Texans presumably did not spend a first-round pick on a rotational player, so Whitney Mercilus will have every opportunity to win a starting outside linebacker job in training camp.
Predicted Winner: Whitney Mercilus
Even though Peter Konz played center at Wisconsin, he will compete for the starting guard position with Mike Johnson as the incumbent Todd McClure starts at center.
Despite being picked in the second round, Konz is a first-round talent who should get the starting job. Johnson, a former third-round pick who has struggled to get onto the field, will likely be the backup.
Eventually, Konz is expected to take McClure's job at center, either late this year or next season.
Predicted Winner: Peter Konz
Once an up-and-coming guard prospect, Mike Pollak has been disappointing so far in his career.
He will have to turn things around quickly, because Amini Silatolu was not a second-round pick so that he could sit on the bench. Silatolu is a mauler in the run game and fits what the Panthers do perfectly.
If Pollak experiences a career rebirth, he stands a chance to win the job, but it seems unlikely at this point.
Predicted Winner: Amini Silatolu
Because of the limited number of draft picks available to the Saints, there's not going to be too much juicy competition this summer.
However, the fourth receiver spot is up for grabs. Nick Toon was one of the steals of the draft, and with great size and route-running ability, he has a great chance of taking the spot.
Joe Morgan, however, has a lot of ability that has been hampered by injury. He had a great preseason before a knee injury landed him on IR, so Toon will have his hands full competing for the fifth spot in camp.
Predicted Winner: Nick Toon
While LeGarrette Blount is certainly an effective downhill runner, he brings little else to the table. He's no use in the passing game and is a huge liability in protection, making him almost useless on third down.
Doug Martin, on the other hand, excels in all areas of his game. He has great hands and takes pride in being reliable as a pass protector.
Martin should immediately take over the third-down role and assume the starting job sooner than later, relegating Blount to relief duties.
Predicted Winner: Doug Martin
Now that the Chiefs have solidified their tackle position after acquiring Eric Winston, all that's left to do is find a starter at one of the guard positions.
The incumbent Ryan Lilja had a down year in 2011, causing the Chiefs to respond by selecting Jeff Allen in the second round of the draft.
Unless Lilja returned to 2010 form, it was expected for Allen to assume the starting role, but an ankle injury may hold him back from getting off to a fast start and open the window for Lilja to retain his starting job.
Nonetheless, even if Allen does not win the job in camp, it's likely that he will take over at some point during the season anyway.
Predicted Winner: Jeff Allen
There are going to be more changes in Denver than just at the quarterback position.
Last season, J.D. Walton was rated as the worst center in the NFL by Pro Football Focus. The Broncos responded by drafting Philip Blake, who has all of the skill to start immediately.
Unless Walton has a career resurrection, Blake has an easy road to win the starting job early in camp.
Predicted Winner: Philip Blake
Despite the fact that the Chargers signed Jarret Johnson away from the Ravens on a four-year deal, they simply could not pass up on the value Melvin Ingram presented in the draft.
While Johnson is the superior run defender and is an underrated pass-rusher in his own right, Ingram has a ton of upside with his athleticism and natural ability. Ingram is also more versatile and can play just about anywhere along the defensive front seven.
However, even if Ingram is impressive in training camp, the Chargers did not sign Johnson to be a backup. Ingram will see the field in passing situations, but Johnson will get the starts in the base defense.
Predicted Winner: Jarret Johnson
Just like the Saints, the Raiders had very little to work with in terms of draft selections this year. They were, however, able to add some receiver depth with the pick of Juron Criner in the fifth round.
Criner had a terrific mini-camp that impressed his teammates, which immediately put Louis Murphy on notice that there will be serious competition for the fourth receiver spot in training camp.
Murphy has been a solid player over the past few seasons for the Raiders in his own right and is certainly good enough to be a fourth receiver on most teams, but if Criner keeps making plays in training camp, it's going to be tough to keep him on the bench.
More often than not, the coaches will give the edge to the younger player with more upside.
Predicted Winner: Juron Criner
The Seahawks clearly want to have an identity of a run-first team, as evidenced by the selection of Robert Turbin.
However, the Seahawks already have Leon Washington on the roster, who, while great in the return game, has not quite been the dynamic player he was with the Jets.
Turbin is a more complete back with less wear and tear on his legs. Assuming he's not a total bust, he should win the starting job rather handily, and Washington will be preserved for his role in the return game.
Predicted Winner: Robert Turbin
Actually, both of these players will start on the Cardinals offensive line. The question is whether to put Massie on the left or right side of the line.
Brown was one of the worst starting offensive linemen in football for the majority of last year, yet he was given an extension at the end of the season after stringing together a couple of decent starts at left tackle.
Massie, on the other hand, fell to the Cardinals in the fourth round because of questions about his character and work ethic. If the Cardinals can get Massie to play at 100 percent, he's probably the best offensive lineman on the roster.
The Cardinals need to figure out if they should move the more talented Massie to the left side or keep Brown there because he showed some promise at the end of last year. I expect Brown to at least get a few starts on the left side before Massie takes over.
Predicted Winner: Levi Brown
After going through a rather ridiculous number of injuries at the corner position last year, the Rams have added several bodies to the position.
Cortland Finnegan will instantly become one of the starters, but the position opposite him remains wide open.
Second-round pick Janoris Jenkins appears to be the favorite to take over. Judging by talent alone, he's arguably the best cover corner in the draft, but concerns about his character caused him to fall on draft day to the second round.
Trumaine Johnson, on the other hand, was selected a round later. While not as talented as Jenkins, he does not have the same off-field concerns as Jenkins.
As long as Jenkins stays out of trouble, this spot should be his in no time.
Predicted Winner: Janoris Jenkins
While Anthony Dixon is a very solid player and a perfectly capable backup to Frank Gore, few players bring the kind of game-breaking ability to the table that LaMichael James does.
This battle is going to come down to how quickly James is able to learn how to pass-protect in the NFL. Rookie runners often have a tough time adjusting to this newer phase of the game, and because James is expected to play a huge role catching the ball in space, he must prove that he's not a liability when asked to stay in and block.
If all goes according to plan and James picks up the offense in time, I don't see how Jim Harbaugh can keep him off the field.
Predicted Winner: LaMichael James