The Baltimore Orioles are one of the oldest institutions in professional sports, operating as a Major League Baseball franchise off and on since the 19th century. But the club's future in Charm City is in question for the first time since it returned to the American League in 1954.

The Orioles currently play at Oriole Park at Camden Yards in Downtown Baltimore, where the team's lease ends in 2021. The sons of principal owner Peter Angelos, who at 90 is in poor health, are mulling the future of the franchise and are leaning toward a sale of the team, the Baltimore Post-Examiner reports, citing anonymous sources.

Another possibility, according to the Post-Examiner, is that John Angelos, one of Peter's sons, would move the club to Nashville, where he and his wife, Georgia, have a home.

If the family finds a buyer, it's no guarantee that entity would hope to keep the team in Baltimore, either — major sports teams rarely hit the market, especially ones with as flexible of a stadium future. In the MLB, only the San Diego Padres, Miami Marlins, Texas Rangers, Houston Astros and Seattle Mariners have sold in the last decade.

Nashville currently doesn't have an MLB team, but it does have a large facility: Nissan Stadium, which seats more than 69,000 and is currently home to the NFL Tennessee Titans (the Orioles' current home has a capacity of nearly 46,000).

Such a move would leave Camden Yards in Baltimore, which opened in 1992 as a pioneering example of a retro-style ballpark, bereft of a tenant. The stadium is part of the larger Camden Yards Sports Complex, which also includes M&T Bank Stadium, home of the NFL's Baltimore Ravens, as well as two sports-oriented museums.

Not everyone is persuaded that the Orioles are likely to move, however, even if the Angelos family decides to sell. While it is true that the Orioles' lease expires soon, no club can relocate out of its local market without an involved process that hasn't even been started, according to Forbes' Maury Brown.

Namely, a move requires a request for proposal-type process that, when completed, would be subject to a vote of the other owners in the MLB, where it would need a three-quarters majority to be approved.

MLB moves have been rare over the last 50 years compared to other major sports leagues, with only three since 1970, most recently when the Montreal Expos moved to Washington, D.C., in 2005.

By contrast, 12 NBA teams and 10 NFL teams have moved in the last 50 years (including the NFL's Oakland Raiders, who plan to decamp for Las Vegas next year).

Peter Angelos bought the Orioles in 1993 for $173M. Currently, according to Forbes, its value would be about $1.3B, despite the team's abysmal recent performance on the field and at the gate. They have the second-worst record in baseball this year, and the third-lowest attendance, according to ESPN.

Nashville, in addition to the Angelos connection, was named by MLB Commissioner Rob Manfred as a candidate for an expansion franchise, and a Nashville businessman is pushing to form a coalition to lure an MLB team to the city, the Nashville Business Journal reported.