It can be a surprising thing when a legitimate NFL star gets traded during the offseason. Sometimes such deals come together quickly and unexpectedly, like the New York Giants' decision to move Odell Beckham Jr. two offseasons ago. Other times, they're planned in advance, like the Detroit Lions' trade of Matthew Stafford earlier this year.

However, even when a trade seems to be lingering on the horizon, the reality of it actually taking place comes as a shock.

In many cases, though, trades don't catch the star players involved completely unawares. Whether due to existing rumors, logical team or salary-cap circumstances or a lack of chemistry with the front office, some players should enter the offseason on trade watch.

We're going to examine seven such players here, along with the reasons they may be moved in the coming months, though there's no guarantee that all or any of them actually will be. We'll be looking specifically at standout players with multiple Pro Bowl or All-Pro appearances on their resumes. Players are listed in alphabetical order.

Derek Carr:

We'll kick things off with a look at Las Vegas Raiders quarterback Derek Carr, who has seemed to be the topic of trade rumors ever since Jon Gruden took over as head coach in 2018. The latest rumor involving Carr also involves a potential Raiders pursuit of Houston Texans star Deshaun Watson.

"Several NFL insiders expect the Raiders to field calls from teams inquiring about Carr's availability," Vincent Bonsignore of the Las Vegas Review-Journal wrote. "Increased demand for his services, insiders say, could create a scenario in which a three-team trade allows the Raiders to acquire Watson."

Carr was more than serviceable as a starter in 2020, ranking 11th in passing yards, 11th in passing touchdowns and 10th in passer rating among full-time starters. But it seems clear that Las Vegas believes it can do better at the quarterback position.

Whether the Raiders do try to acquire Watson from Houston or turn their attention to the upcoming draft—Las Vegas currently picks 17th overall but could theoretically move up significantly with a trade—Carr could be shipped out. At the very least, he cannot take a starting job with the Raiders in 2021 as a given.

Zach Ertz:

Based on his emotional reaction to the Philadelphia Eagles' loss in Week 17, tight end Zach Ertz probably already senses that a trade or release is in the works.

"This city means a lot to me, means a lot to my family, and I'm thankful," he told reporters after the game.

A trade would make sense for the Eagles because they could get something in return and save nearly $5 million in cap space. There's a good chance a team would be willing to part with assets to obtain the three-time Pro Bowler rather than risk chasing him on the open market.

There's a possibility too that the Eagles could include Ertz as part of a package to trade quarterback Carson Wentz. The Eagles have been looking to deal the much-maligned signal-caller but are "still waiting" for a deal they feel is adequate, according to NFL Network's Mike Garafolo (h/t Michael David Smith of ProFootballTalk).

With only one Pro Bowl to his credit, Wentz doesn't qualify as a "star" for this list's purposes, though he should indeed be bracing for a trade. Perhaps including Ertz in a deal could help get it done.