SANTA CLARA, Calif. (AP) — Whether it's star players holding out of training camp or holding in by reporting and not practicing, contract disputes are playing a prominent role across the NFL this summer.

Some of the top contenders to compete for the Super Bowl are headed into the first full weekend of exhibition games with some of their most important players unwilling to take the practice field before they get new contracts.

The issue is most prevalent in San Francisco, where the defending NFC champion 49ers are preparing for the season with second-team All-Pro receiver Brandon Aiyuk refusing to practice unless he gets a new contract or is traded and All-Pro left tackle Trent Williams back at home in Texas waiting for a new deal.

The frustration level is growing for the 49ers, who have given Aiyuk's representatives permission to seek out a possible trade with no resolution so far more than two weeks into camp.

Aiyuk is attending meetings and even has been out watching practice — and exchanging hugs and handshakes with coach Kyle Shanahan and general manager John Lynch — as he avoids daily fines of $40,000 for players on rookie contracts by being in camp.

Williams is being fined $50,000 a day for holding out but Shanahan sees little practical difference in the two approaches since neither player is actually practicing.

"It’s nice not fining guys, but there’s not much of a difference,” he said.

Two other star receivers are in similar situations to Aiyuk with Dallas' CeeDee Lamb holding out of Cowboys camp and Cincinnati's Ja'Marr Chase “holding in” with the Bengals.

Shanahan isn't the only one bewildered by the process. Lamb responded with an "lol" on social media Thursday to a post quoting Dallas owner Jerry Jones saying he had no “urgency to get it done.”

The other prominent contract holdout this summer is edge rusher Haason Reddick, who has refused to report to the New York Jets after being acquired in the offseason in a trade from Philadelphia.

Here's a look at the key holdouts and “hold ins” this summer:

Brandon Aiyuk

San Francisco's top wideout has been looking to get paid that way this offseason instead of playing out the fifth year worth about $14.1 million. Ten receivers have signed contracts this offseason worth at least $70 million, with Justin Jefferson’s four-year, $140 million extension with Minnesota setting the top of the market.

Aiyuk's numbers aren't as prolific as some of the top receivers, in part because he plays on an offense that runs at the second-highest rate in the NFL and is filled with other playmakers. But he still managed 75 catches for a career-high 1,375 yards last season with his 12.8 average yards receiving per target the highest mark for any player with at least 75 targets in more than a decade.

Trent Williams

As important as Aiyuk is to San Francisco's offense, Williams is even more irreplaceable with the Niners sputtering in his brief absence last season. Williams has been a first-team All-Pro for three straight seasons and is widely considered the top offensive lineman in the league.

Williams likely wants to get paid that way. He signed a six-year, $138.1 million contract before the 2021 season, making his average annual salary now sixth best among tackles after Tristan Wirfs, Penei Sewell and Christian Darrisaw all signed big-money deals this offseason.

CeeDee Lamb

Lamb is also going into the last year of his rookie contract after being drafted 17th overall in 2020. He led the NFL in receptions last season (135) and was second in yards receiving (1,749) and third in touchdown receptions (12).

Lamb already skipped minicamp in June, a decision that came one day after Jefferson agreed to the most valuable contract for a non-quarterback in league history.

Lamb and Jefferson are effectively neck-and-neck in career statistics after being selected six picks apart in the first round in 2020. Lamb has increased his production each season and was a first-team All-Pro in 2023.

Haason Reddick

The Jets traded for Reddick this offseason without coming to an agreement with him about his contract. Reddick was scheduled to make $14.25 million in base salary in the final year of his deal and has already sacrificed about $1 million in fines and forfeited workout bonuses in search of a bigger contract.

Reddick, a first-round pick by Arizona in 2017, has double-digit sacks in four straight seasons, including 27 during the past two years with the Eagles. He’s expected to boost the Jets’ pass rush while replacing Bryce Huff and John Franklin-Myers on the defensive line.

Ja'Marr Chase

The Bengals came into the offseason with contract issues with both of their star receivers. They didn't reach a long-term deal with Tee Higgins, who signed his franchise tag and is playing out his final year before free agency.

Cincinnati still has control of Chase for longer with a fifth-year option for 2025 and a possible franchise tag after that. But he wants to get paid sooner and is refusing to practice without a deal.

Joe Burrow's former college teammate at LSU has built a great rapport with him in the NFL since being picked fifth overall in 2021.

In three seasons, Chase has 268 catches for 3,717 yards and 29 TDs