FOXBOROUGH, Mass. (AP) — Several NFL owners locked arms with their players this weekend instead of taking a challenge from President Donald Trump to fire them for protesting during the national anthem. NASCAR Hall of Famer Richard Petty said he would get rid of anyone on his racing team who didn't stand.

Neither is surprising.

Both are legal.

Private businesses — including sports leagues — routinely punish employees for things they say or do, even if those comments or actions are otherwise legal. The First Amendment so often cited as a blanket justification for "free speech" doesn't protect the employment of football players or racecar drivers when they speak their minds.

As the Supreme Court Justice Oliver Wendell Holmes once said, "A policeman may have a constitutional right to talk politics, but he has no constitutional right to be a policeman."

So why did NFL owners — many of them Trump supporters — back their players instead of their president?

It's business.

Here are a few more questions and answers about the potential consequences of the NFL anthem protests:

WHAT DOES THE CONSTITUTION SAY?

The right to free speech is defined in the First Amendment, which reads: "Congress shall make no law ... abridging the freedom of speech, or of the press."

Don't ignore the first part: It's the government that can't restrict speech. In other words, out-of-work quarterback Colin Kaepernick can't be thrown in jail for kneeling during the anthem, but the constitution doesn't guarantee him a spot on an NFL roster.

So U.S. Treasury Secretary Steven Mnuchin had the law on his side when he said of the protesting football players, "They can do free speech on their own time."

WHAT ARE PLAYERS REQUIRED TO DO?

The rules governing NFL player conduct are spelled out in its rulebook , its personal conduct policy , and the collective bargaining agreement negotiated between the league and its union.

The rulebook is very specific about what constitutes an excessive touchdown celebration, the proper inflation of a football and what kind of logo can appear on a player's shoes. It does not say players must stand during the national anthem.

The personal conduct policy covers activities that might be criminal — domestic or workplace violence, illegal gun possession, cruelty to animals — regardless of whether they result in a conviction or even criminal charges. (It also says players do not have protection against self-incrimination when they are investigated by the league, so there goes the Fifth Amendment, as well.)

The CBA has two references to pre-game activities and neither involves the anthem or the flag. (One requires players to be given breakfast money if the pre-game meal comes after 9 a.m.)

SO THEY'RE SAFE?

Nope.

The NFL's CBA also includes a boilerplate contract that requires not only a player's best efforts on the field but also "loyalty to the Club, and to conduct himself on and off the field with appropriate recognition of the fact that the success of professional football depends largely on public respect for and approval of those associated with the game."

This gives the league wide latitude in punishing players for behavior that might damage the sport's reputation — anything from illegal (or even legal) gambling to comments that might scare off sponsors or fans.

Other sports have similar leeway.

Former baseball commissioner Bud Selig used his "best interests of the game" powers when he suspended Atlanta Braves reliever John Rocker in 1999 for racist comments in a magazine article. The NBA relied on its own constitution when it banned Los Angeles Clippers owner Donald Sterling for life and stripped him of his team in 2014, also for racist comments.

NASCAR contracts aren't standardized, but an employee manual for the now-defunct Michael Waltrip Racing reminded workers that they are hired at-will and can be fired "at any time for any reason or for no reason." In the section regarding substance abuse, the employee acknowledges that: "The Company reserves the right to take any action against an employee ... whose conduct is deemed detrimental to the Company."

So race team owner Richard Childress was likely within his rights when he warned employees considering an anthem protest: "It'll get you a ride on a Greyhound bus."

(But Petty went too far when he said: "Anybody that don't stand up for the anthem oughta be out of the country. Period.")

SO, WHAT'S GOING TO HAPPEN TO THOSE FOOTBALL PLAYERS?

Kaepernick, who started the movement by kneeling during the anthem last season, remains without a team. The league denies he is being blackballed, but several less accomplished quarterbacks — some starters, many backups — have found NFL jobs.

Don't expect to see other protesters purged, though.

For one thing, there are now too many of them. More importantly, the league and its owners decided that standing with the players was good for business — not just keeping the workforce happy, but also trusting that fans and sponsors would stick around.

NASCAR bosses came to the opposite conclusion.

It's not surprising.

It's not illegal.

It's business.

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Jimmy Golen covers sports and the law for The Associated Press.

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AP Auto Racing Writer Jenna Fryer contributed to this story.