It happens every year. Players emerge seemingly out of nowhere during training camp and go on to not only make the team, but have a sizable impact during the regular season. Who will those players be this year? We list five veterans who have a chance to break out and earn increased roles with the team.
I left Dontrelle Inman and Cordarro Law off this list, even though they both qualify, because we've already covered them in this feature on San Diego's Canadian imports.
CB Richard Crawford
The Chargers signed Crawford as a street free agent last October. He spent his first season in San Diego bouncing back and forth between the active roster and practice squad.
A seventh-round pick of the Redskins in 2012, Crawford made an immediate impact as a rookie. He appeared in 10 games and improved as the season progressed. In the season finale against the Cowboys, he had an interception and two pass breakups to help send the Skins into the playoffs.
Crawford is also a weapon on special teams. As a rookie he returned eight punts for 156 yards (19.5-yard average), including a 64-yard return that facilitated an overtime win over the Ravens.
Unfortunately, he tore his ACL and LCL the following preseason. The injury wiped out his entire 2013 season and limited his explosiveness last year.
It has now been nearly two years since Crawford's devastating injury and he is again looking like his old self. There is competition in San Diego's secondary -- Patrick Robinson, Craig Mager and Steve Williams are also jockeying for the nickel and dime roles -- but playmakers like Crawford are difficult to dismiss.
WR Austin Pettis
The Chargers added a couple veteran receivers via free agency in Stevie Johnson and Jacoby Jones. That makes it easy to forget about Pettis, who signed with the Chargers shortly after last season finished.
A third-round pick of the Rams in 2011, Pettis averaged 31.6 catches over his first three seasons. However, he fell out of favor last season and got lost in the shuffle of St. Louis' recent draftees; the Rams spent six draft picks between 2011-2013 at the wide receiver position, all in the fourth round or higher.
Pettis faces tough odds to stick in San Diego. In addition to the newcomers mentioned above, the Chargers also need to make room in the rotation for Inman, who proved he belongs with his big games late last year.
Nonetheless, the Chargers have had a tough time keeping all their receivers healthy. Keenan Allen was unavailable late last season due to a broken collar bone, while Malcom Floyd has played in all 16 games just twice in his 11-year career. Having a veteran like Pettis around provides valuable insurance and should force all of San Diego's receivers to elevate their games.
OG Craig Watts
Watts is the youngest player on this list. He was a rookie just last year, when he spent the season on the Bolts' practice squad. The mauler from West Texas A&M is expecting bigger things in 2015 and may get a chance to compete for a starting spot.
Watts (6'4, 335 lbs.) is a powerful blocker with an impressive ability to pull and make blocks in space. His nimbleness comes from his soccer background; as a military brat, he grew up in Germany and spent most of his life playing soccer.
Watts did not start playing football until his junior year of high school, so he still has plenty of room to grow. It helps that he has been like a sponge since joining the Chargers, proving to be one of the team's most coachable and determined players.
With a strong training camp, Watts projects as the top backup guard behind Orlando Franklin and Johnnie Troutman (or D.J. Fluker). Watts will have a chance to unseat Troutman from the starting lineup if Fluker remains at tackle.
DT Damion Square
The Chargers added some depth to their defensive line this offseason by signing free agent Mitch Unrein and drafting Arkansas' Darius Philon. But don't count this holdover out of the mix just yet.
Square was part of a dominant Alabama defensive line that included Marcell Dareus and Terrence Cody. And while he is not as imposing as those two, he also doesn't get caught with marijuana or abuse alligators, so you take the good with the bad.
Square started all 13 games each of his final two seasons at Alabama, saving his best work for his senior year (33 tackles, 3.5 sacks, four TFLs and a forced fumble). It was enough to get him noticed by the Eagles, who signed him as an undrafted free agent following the 2013 draft.
Square appeared in 10 games as a rookie with the Eagles. He was chopped in the final round of cuts before his second season and then spent a cup of coffee in Kansas City before catching on with the Chargers.
There are no studs on San Diego's defensive line other than Corey Liuget. Square will be given every opportunity to prove he deserves a spot in the rotation. His motor, versatility and strength give him a legitimate shot to stick.
QB Brad Sorensen
The Chargers were extremely high on Sorensen during his promising rookie season. The 2013 seventh-round pick showed good accuracy and an impressive command of the offense, even forcing Chargers coaches to consider making him the No. 2 quarterback ahead of Charlie Whitehurst.
Last year, things did not go so well. Sorensen struggled in the preseason. He played most of the third preseason game in San Francisco and completed just 11 of 21 passes (52.4 percent) with two interceptions. He failed to survive the final round of cuts and went on to spend some time with the Titans before rejoining San Diego's practice squad late in the year.
What makes Sorensen worth watching is the Chargers are now being forced to consider the future of the quarterback position. Philip Rivers, 33, is entering the final year of his contract and is reluctant to sign an extension. That means the Chargers could give Sorensen a longer look during training camp and the preseason to see if he is ready to assume a larger role.
Sorensen is a smart player with a good arm and the ability to drive the ball down the field. He is also at his best when working from the shotgun in a wide-open offense, which is something the Chargers run often. Perhaps in his third season -- and with an improved supporting cast -- Sorensen can put it all together and start working his way back up the ladder.
Which players do you see making San Diego's Opening Day roster? Talk about it in our message boards!
Michael Lombardo has covered the San Diego Chargers since 2003. He spent 12 years covering the team for Scout.com and has been published by the NFL Network, Fox Sports and MySpace Sports. In addition to being publisher of SDBoltReport.com, he also works as the Senior NFL Reporter for Footballinsiders.com. You can see more of his updates by following him on twitter.