It’s summertime and the heat’s on these quarterbacks

As if replacing a legend weren’t tough enough, Green Bay quarterback Aaron Rodgers faces an even more difficult challenge.

He’s replacing Brett Favre, a legend who wants to come out of retirement and play again.

But Rodgers isn’t the only young quarterback under pressure this season. As training camps open all over the NFL this week, a host of signal-callers are under scrutiny.

A look at some of them:

Matt Leinart, Arizona -- The starting job is Leinart’s to lose, but Kurt Warner is peering directly over his surgically repaired shoulder. And Warner, who’s paid like a starter, did a tremendous job filling in for the injured Leinart last season, throwing for 27 touchdowns with 17 interceptions.

Arizona coaches thought Leinart could have prepared better for last season’s opener against San Francisco, and are expecting more focus from him this season. They don’t want to see any more party pictures of him on the Internet, and are ready for him to make good on all the promise he showed as a USC star.

Jason Campbell, Washington -- New coach, new system, old problem: round peg in a square hole. Campbell has a big arm but has struggled with short-range accuracy and touch. Jim Zorn, new Redskins coach, wants to transform him into a West Coast-style quarterback.

Campbell is very talented and a hard worker, so it just might work. But it won’t be easy. Meanwhile, Todd Collins, the player who led Washington to the playoffs last season when Campbell was hurt, is watching from the sideline and ready to step in.

Alex Smith, San Francisco -- Smith, selected first overall in 2005, is by no means the guaranteed starter. He and Shaun Hill will be trading snaps during camp, and Coach Mike Nolan says he won’t name the starter until the third exhibition. Even journeyman J.T. O’Sullivan has an outside chance of earning the job.

If Smith has fallen short of being San Francisco’s savior -- and the stats say that’s the case: 44 turnovers vs. 19 touchdowns -- it’s not entirely his fault. He’s worked with four offensive coordinators in four seasons.

Joe Flacco, Baltimore -- Big things are expected from Flacco, the rookie from Delaware with the Ben Roethlisberger-like throwing arm. But the heat won’t be on him right away; he’ll be competing for the starting job with Kyle Boller and Troy Smith -- unless the Ravens happen to pull off a trade for Favre.

Eventually, though, Flacco will get a chance to show that he’s worth the robust deal the Ravens gave him, one that could be worth $30 million and includes an $8.75-million bonus. Coming from a relatively small school, he thinks he has something to prove.

Matt Ryan, Atlanta -- Not only is the rookie facing the scrutiny that comes with replacing Michael Vick, but he’s challenged with playing up to his gargantuan contract.

Ryan’s six-year, $72-million deal includes $34.5 million in guaranteed money, the most ever committed to a rookie.

His contract comes at a time when even NFL Commissioner Roger Goodell is questioning the fairness -- and sanity -- of giving such blockbuster deals to players who have never taken a snap as a pro.

Tavaris Jackson, Minnesota -- Lost in all the talk about the Vikings’ alleged flirtation with Favre is that Jackson had a promising spring. Still, many people regard him as the weak link on a team with top-shelf talent at lots of other positions.

Teammate Darren Sharper, who has been training with Jackson and new Vikings receiver Bernard Berrian, told the St. Paul Pioneer Press that the young quarterback has been making some All-Pro throws lately.

“T-Jack is our guy,” Sharper said on the newspaper’s website. “I have the utmost confidence in Tavaris.”

Brady Quinn, Cleveland -- OK, so Quinn isn’t the starter. Derek Anderson proved last year that he deserves that job, and the Browns said as much by rewarding him with a three-year, $26-million contract extension. But that doesn’t erase the fact that 2007 first-rounder Quinn is waiting in the wings.

At some point, the Browns are going to have to figure out what they have in Quinn -- and that’s likely to start this summer. A camp holdout a year ago, Quinn missed 11 days of training camp and took only 10 snaps during the regular season. This summer, he should get a chance to show his team and others that he’s capable of getting the job done.

JaMarcus Russell, Oakland -- Although he’s in his second season, Russell is a rookie to training camp. His holdout last summer stretched into the second week of the regular season. Now, he’s the designated starter, and the Raiders don’t have the fallback of experienced veterans behind him. Gone are Daunte Culpepper and Josh McCown, and in their place are Marques Tuiasosopo and Andrew Walter, who have a combined 10 career starts.

Good news for Russell: Having explosive ballcarriers Darren McFadden and Justin Fargas is sure to make his job easier.

Rex Grossman, Chicago -- On one hand, the Bears should be applauded for their loyalty. On the other, how much is too much? Chicago has to get consistent production out of Grossman, or bench him in favor of Kyle Orton.

The club passed on a chance to draft a top quarterback prospect this year, instead taking tackle Chris Williams in the first round and running back Matt Forte in the second. But it’s not as if a guy like Favre is going to fall in their laps. . . . Would he?

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sam.farmer@latimes.com