In March, NFL owners locked out their players. On Friday, NBA owners followed suit.

It's believed that only once before two of the United States' major sports leagues have been shuttered at the same time.

A look at what's at stake in the labor disputes, and how they are similar and different:

Q: What's with the NFL and the NBA being stuck in labor lockout at the same time? Are the two situations connected?

A: It's partly a coincidence that the two leagues' collective bargaining agreements expired within months of each other. But it's probably not a fluke that owners in both sports are saying at the same time that the old deals didn't provide them with sufficient revenue. The U.S. economy is emerging from a recession. And NFL and NBA leaders contend there aren't enough new revenue streams to cover costs for building and improving stadiums and arenas.

Q: But haven't both sports being doing very well recently?

A: The NFL and NBA have enjoyed a surge in interest the last couple of seasons, with appealing story lines and big-name stars driving robust television ratings. In fact, the two most watched U.S. television programs of all time were the past two Super Bowls. And the NBA, while not the same draw as pro football, last month had the highest rating for a Game 6 of its final series in 11 years.

Both players' associations argue that's proof the leagues are better off than they purport to be. The owners counter that ratings and other indicators of popularity are irrelevant when their economic models are broken. NBA owners say they lost hundreds of millions of dollars in every season of the last collective bargaining agreement, which was ratified in 2005. According to league officials, 22 of the 30 teams were losing money this past season. One of the points of contention between the NFL and its players is that the union wants access to more financial data from teams to see the exact economic situation of the clubs.

Q: OK. But what, exactly, is a lockout? And how's it different from a strike?

A: Management has the right under federal labor law to shut down a business once a CBA expires. That means, for instance, that the leagues aren't paying for players' health insurance, and free agents can't sign with teams. Employees have the same right to strike.

In this case, for both basketball and football, the owners' side is the one that wants to significantly alter the structure of the old deal, leading to a lockout, not a strike.

Q: How similar are the issues in the two sports' negotiations?

A: The tone of the two labor disputes has differed because of the league's disparate financial situations. For the NFL, the debate is how to divvy up $9 billion in revenues, with players and owners wrangling over what is the fairest split. The NBA is in a more dire economic plight, and the question is how much of a hit players' salaries will take as a result.

Q: Is the NBA lockout going to look like the NFL's?

A: The NFL union decertified and turned to the courts in an attempt to lift the lockout. The NBA players' association doesn't plan to go that route, at least for now.

Q: Should fans be worried about losing games in either situation?

A: Anything's possible. There was optimism earlier this week that an NFL deal was near, but the sides went into the holiday weekend without an agreement. The league says it hasn't set a deadline for when games would be canceled without a CBA. The regular season is supposed to start Sept. 8, but the NFL could start later and still get in 16 games. The NBA's regular season isn't scheduled to start until around late October, but at the moment both sides say they're very far apart.

Q: Are NFL or NBA players looking for jobs in other leagues?

A: NFL players don't have the sort of high-paying options NBA players do overseas. For example, guard Sasha Vujacic, who played for the New Jersey Nets last season and now is a free agent, said Saturday he would be open to signing with a team in Europe or China. "Definitely, as players, we've got to look at other opportunities," he said.