Lots of players have a no-trade clause. None, as far as we know, have a must-trade provision in their contract.
Still, every once in awhile, a player will conclude that on the whole, he'd rather be, well, somewhere other than where he is. Already this offseason, Christian Yelich and J.T. Realmuto of the Marlins have suggested they might be happier elsewhere in the wake of the team trading Giancarlo Stanton to the Yankees, Marcell Ozuna to the Cardinals and Dee Gordon to the Mariners.
The latest to float that particular trial balloon is Pirates infielder Josh Harrison. After center fielder Andrew McCutchen was traded to the Giants and right-hander Gerrit Cole to the Astros over the past week, Harrison suggested through The Athletic website that "perhaps it would be better for all involved" that he also be moved.
To be clear, Pirates general manager Neal Huntington has denied the Bucs are in a rebuilding mode. And players have no formal mechanism to force a trade.

On the other hand, teams are often reluctant to have a guy in the clubhouse who has made it clear he'd prefer not to be there. And Harrison, a two-time All-Star, has some value. So for the sake of discussion, let's assume that Huntington will now pick up the phone and investigate whether there's a deal to be made that would satisfy all concerned.
First, the particulars. Harrison is 30 years old. He started 79 games at second last season, 37 at third and nine in the outfield. Harrison had a .771 OPS with a career-high16 homers, and he's considered an above-average defender. He'll make $10.25 million this season, with two club options, for $10.5 million in 2019 (or a $1 million buyout) and $11.5 million in 2020 (or a $500,000 buyout).
Given all that, what teams might be interested if the Pirates did decide to shop Harrison?
The most logical landing spot would seem to be the Mets, who have Gavin Cecchini as their likely starting second baseman. The 24-year-old has just 36 games of big league experience.
Mets general manager Sandy Alderson had been looking into acquiring a veteran second baseman even before Harrison's trade request. New York had reportedly asked about Ian Kinsler before the Tigers traded him to the Angels, and the Mets are also rumored to have been in talks with the Indians about Jason Kipnis.
So Harrison makes sense. Alderson, however, has said he'd lean toward signing a free agent rather than giving up prospects, and there are several options still available on the market, including Todd Frazier, Neil Walker, Eduardo Nunez and Brandon Phillips. The scuttlebutt is that promising outfielder Brandon Nimmo would have to be part of any deal for Harrison.
Meanwhile, in the Bronx, the Yankees are also thinking about adding some experience to an infield that has rookie Miguel Andujar penciled in at third and 25-year-old Ronald Torreyes at second, with rookie Gleyber Torres also in the mix. The Yanks have had a lot of success with young players like Aaron Judge and Gary Sanchez the past couple seasons, but general manager Brian Cashman might feel more comfortable with a veteran option.
Walker left the Brewers, who finished a strong second in the National League Central last season, as a free agent. That leaves Eric Sogard and Jonathan Villar, but there has been speculation that the Crew might kick the tires on Harrison.
There don't appear to be other teams looking for help at second base, but the fact that Harrison can also play third could expand the market.
The White Sox and Braves might consider adding an established veteran at the hot corner. If the Royals don't end up re-signing Mike Moustakas, Kansas City could be an option. And the Orioles have had some talks about trading Manny Machado before he becomes a free agent; if something comes together, that could create an opening in Baltimore.
And, of course, there's always the possibility that Harrison might stay right where he is.