National Football League stars past and present are expressing outrage after President Donald Trump used an address in Huntsville, Alabama, on Friday to attack players who protest during the national anthem.

During what was supposed to be a stump speech for Sen. Luther Strange (R-Ala.), Trump drifted away from campaigning to ask members of the crowd if they’d “love to see one of these NFL owners, when somebody disrespects our flag, to say, ‘Get that son of a bitch off the field right now, he’s fired’?”

He also encouraged fans to boycott the league over the protests.

Trump did not reference by name San Francisco 49ers former player Colin Kaepernick, who took a knee during the national anthem before games last year to protest police brutality and racial injustice.

But his comments were interpreted as a thinly veiled attack on the athlete, who remains a free agent, and other players he has inspired to take similar action.

Seattle Seahawks cornerback Richard Sherman, wide receiver Doug Baldwin and former running back Reggie Bush were among those to call out Trump for his remarks:

The behavior of the President is unacceptable and needs to be addressed. If you do not Condemn this divisive Rhetoric you are Condoning it!! — Richard Sherman (@RSherman_25) September 23, 2017

#Seahawks WR @DougBaldwinJr official statement to me on Donald Trump's remarks on national anthem protests in the @NFL. pic.twitter.com/pPA6ZR6UcB — Josina Anderson (@JosinaAnderson) September 23, 2017

I can’t take anything our Celebrity in Chief says seriously. He’s a real life clown/troll 🤡 — George Iloka (@George_iloka) September 23, 2017

#Kaepernick we riding with you bro ✊🏾 — Reggie Bush (@ReggieBush) September 23, 2017

When will people learn that fear won’t make someone sit down. It quite possibly will make more stand up for what they believe in. — Chris Conley (@_flight17_) September 23, 2017

My mom is a beautiful lady she has never been a bitch — Michael Bennett (@mosesbread72) September 23, 2017

It's a shame and disgrace when you have the President of the US calling citizens of the country sons of a bitches. — Bishop Sankey (@BishopSankey) September 23, 2017

cloth has more value than people. apparently. https://t.co/PZjeRA9861 — feeno (@ArianFoster) September 23, 2017

I'm a full supporter of the Flag & This country! Trust Me! But this can't be real! https://t.co/GAPkZPB8hz — Rishard Matthews (@_RMatthews) September 23, 2017

Trump!! 😔😔😔😔😔😔😔 — Thomas Davis (@ThomasDavisSDTM) September 23, 2017

Does anyone tell trump to stick to politics, like they tell us to stick to sports? Smh. — Eric Ebron (@Ebron85) September 23, 2017

Trump stay in ur place... football have nothing to do wit u smh — Zach Brown (@ZachBrown_55) September 23, 2017

They really let Trump do and say whatever TF he wants. Shit is crazy. — Matthew A. Cherry (@MatthewACherry) September 23, 2017

DeMaurice Smith, the executive director of the NFL Players Association, also made his position crystal clear via this statement on Twitter:

We will never back down. We no longer can afford to stick to sports. pic.twitter.com/Ec3Bc4qt9h — DeMaurice Smith (@DeSmithNFLPA) September 23, 2017

NFL Commissioner Roger Goodell also released a statement in which it said that “divisive comments like these demonstrate an unfortunate lack of respect” for the league and its players.

New NFL statement pic.twitter.com/XHPgVvPPfH — Brian McCarthy (@NFLprguy) September 23, 2017

Stephen Ross, owner of the Miami Dolphins, said that he personally knows some of the NFL players who are protesting and said they were “smart young men of character who want to make our world a better place.”

He called for “unifying leadership” and “civil discourse” instead of “condemnation and sound bites.”

Statement from Miami Dolphins Owner and Founder of Ross Initiative in Sports for Equality (RISE) Stephen Ross. pic.twitter.com/6W3mXwJO6M — Miami Dolphins (@MiamiDolphins) September 23, 2017

Hundreds of other tweeters joined in with blasting Trump, with many accusing him of trying to prevent people from exercising their First Amendment rights.

The hashtag #takeaknee also began trending globally on Twitter.

Check out a sampling of the other responses below:

"Get that son of a bitch off the field"- black man protesting racial injustice



"Very fine people"- white people demanding racial injustice — Jared Rizzi (@JaredRizzi) September 23, 2017

Get that son of a bitch off the stage. — Samuel Sinyangwe (@samswey) September 23, 2017

Black man uses his position to draw attention to a controversial, important issue.



White president calls him a son of a bitch. — Scott Weinberg (@scottEweinberg) September 23, 2017

Can't wait to see Trump pallin' around with NFL owners after he said NFL employees who exercise their first amendment rights should be fired — Charlotte Wilder (@TheWilderThings) September 23, 2017

Let me be REAL clear: @realDonaldTrump just guaranteed that more heat is about to be unleashed on the @NFL. The players WILL respond! https://t.co/4FOQXRiTFz — rolandsmartin (@rolandsmartin) September 23, 2017

Add “black NFL players exercising their First Amendment right” to the list of people Trump has criticized more harshly than Vladimir Putin. — Rex Huppke (@RexHuppke) September 23, 2017

Trump a lot tougher on Colin Kaepernick than on Vladimir Putin. Protesting American anthem: bad. Subverting American democracy: no big deal. — Max Boot (@MaxBoot) September 23, 2017

Trump was quicker and more vehement in his hatred of Colin Kaepernick’s non-violent protest than he was of Nazis. Take note of that. — Anthony F. Irwin (@AnthonyIrwinLA) September 23, 2017

I'm like 75% sure that if Trump had never talked about Kaepernick he'd be on a roster now https://t.co/UMN96YttkU — Matthew Zeitlin (@MattZeitlin) September 23, 2017

Government figure says he hates when people exercise their Constitutional right to free speech: pic.twitter.com/GCIS9CMLSY — jordan 🌹🌹 (@JordanUhl) September 23, 2017

.@realDonaldTrump has attacked Colin Kaepernick with more conviction than he has NAZIS. 🤔 — Michael Skolnik (@MichaelSkolnik) September 23, 2017

To be clear, Colin Kaepernick's "crime" is protesting systemic racism and police brutality. Trump called him a "son of a bitch" tonight. — Ben Gardner (@BenGardner87) September 23, 2017

Donald Trump has gone after Jemele Hill and Colin Kaepernick stronger than he went after Nazis. — B. 📎 (@knicks148) September 23, 2017

Black man uses his position to draw attention to a controversial, important issue.



White president calls him a son of a bitch. — Scott Weinberg (@scottEweinberg) September 23, 2017

Donald Trump referred to Colin Kaepernick as a 'son of a bitch' at his Alabama rally? He didn't even call the #Charlottesville murderer that — Cyrus McQueen (@CyrusMMcQueen) September 23, 2017

This is the President of the United States of America.



Not to mention Kaepernick's not on a team. https://t.co/yidLC53Wwa — mike freeman (@mikefreemanNFL) September 23, 2017

Very revealing that the harshest language Trump has ever used as President was reserved for Black men protesting injustice. https://t.co/v2I6tf5ZHq — Shaun King (@ShaunKing) September 23, 2017

Trump on Kaepernick: son of a bitch!



Trump on Nazis: they're bad but like lol idkhttps://t.co/RUC2BggUAZ — Manny Fidel (@mannyfidel) September 23, 2017

Correction: A previous version of this article misidentified the Brandon Marshall who posted the tweet as being the New York Giants’ wide receiver.