NFL rookies have a lot to learn, and 2015 is no different. Standing on a cafeteria table at training camp and singing their alma mater’s fight song is one of the easier part’s of a rookie’s initiation into the NFL. They have to digest a playbook and execute those plays against players who are a lot better than the ones they faced in college.

Here are five NFL rookies in particular who have a lot to prove entering the 2015 NFL season.

Jameis Winston, QB, Tampa Bay Buccaneers

Being the No. 1 overall pick in the draft automatically plasters Jameis Winston with the “something to prove” label.

But Winston also has to out-run his “crab leg” past. If he can make a few Pro Bowls and turn the Tampa Bay Buccaneers into a Super Bowl contender, no one will care if he stole those crab legs or if he got them for free.

Winston also has the prove he has the character and maturity to be a team leader. He has to show that shouting a sexually explicit remark in the student union at Florida State was the act of an immature college kid and not the sign of a deeper flaw that could cause problems down the road.

Buccaneers center Evan Smith, who also snapped the ball to Aaron Rodgers when he was a Packer, told Yahoo! Sports that Winston reminds him of a young Aaron Rodgers.

That’s not a bad start.

Marcus Mariota, QB, Tennessee Titans

The No. 2 overall pick in the draft, Marcus Mariota has to prove that he can adjust to an NFL playbook.

Mariota won the Heisman Trophy, but didn’t run the offense from under center at Oregon. It won’t be all shotgun in the NFL.

According to NFL.com, Mariota hadn’t thrown an interception in practice as of Tuesday. He’ll be challenged a little more when he faces the Falcons defense for a series or two in Friday night’s preseason opener.

Then the true test will come when the games count.

Marcus Peters, CB, Kansas City Chiefs

Marcus Peters, chosen 18th overall, was moved to the first team at practice according to ESPN.com.

So while he seems to be having a good camp, Peters has to prove that he won’t be a source of headaches for Andy Reid.

Peters admitted to failing a drug test in 2011 and was penalized for head-butting an opponent last season, according to the The Kansas City Star.

Washington head coach Steve Sarkisian went to USC. Peters didn’t mesh well with new coach Chris Petersen and his staff in 2014 and he was thrown off the team in November. Now that he’s in the NFL, he has another big adjustment to make. He’ll have to do a better job this time.

Bud Dupree, OLB, Pittsburgh Steelers

A day before the draft, Bud Dupree was projected to be chosen as high as No. 6 in some mock drafts.

Then on draft day, his stock took a plunge. His freefall ended at No. 22, where the Steelers snapped him up.

The knock on Dupree was a lack of football IQ despite elite athleticism. Despite playing a team-high 45 snaps in the NFL Hall of Fame Game on Sunday, Dupree was barely visible in the Steelers’ 14-3 loss to the Minnesota Vikings.

Not only does Dupree have to prove teams a bunch of teams wrong for passing on him, he also has to prove to the Steelers that he won’t be a bust.

Randy Gregory, OLB, Dallas Cowboys

This rookie joins what seems like a team full of players with something to prove, whether it’s Greg Hardy trying to put his past behind him or Darren McFadden trying to prove he can stay healthy.

Projected as a top-five pick early in the pre-draft process, Gregory admitted to failing two drug tests in 2014 and another one for marijuana at the NFL Scouting Combine.

Down went Gregory’s draft stock, and Jerry Jones and his Cowboys took Gregory with the 60th overall pick in the second round.

Not only is Gregory subject to testing under the NFL’s drug policy, but he also has to show that he’s hefty enough to play defense in the NFL.

According to ESPN.com, the 6’5″ Gregory said he probably weighs somewhere in the 240s (pounds). He weighed just 229, however, when the Cowboys drafted him.

With all that he has to prove, a little extra food is among the many things on Gregory’s plate.