The 22-year-old, a quarter-finalist at the 2019 Australian Open, posted an Instagram video, external also featuring Serena Williams, Naomi Osaka and Coco Gauff.
In the video, Tiafoe and his girlfriend, Ayan Broomfield, put their racquets down and raise their hands to “spread awareness about the unjust deaths of many African-Americans”.
Widespread protests have taken place across 75 US cities since Floyd, an unarmed black man, died after being pinned down by a white police officer.
Minneapolis police officer Derek Chauvin, who kneeled on Floyd’s neck, has been charged with his murder. He and three other police officers have been sacked.
“We start trends: people want to be like a LeBron James, like a Michael Jordan, like a Roger Federer, so when they go and say something, people are going to listen. And those are the things that can really make changes. If they really speak out and make a difference, I think things can happen.”
The video is set to the song Glory. It was written and performed by John Legend and the rapper Common for the film Selma, which documented aspects of the 1960s US civil rights movement.
Sloane Stephens, Gael Monfils, Jo-Wilfred Tonga and Britain’s Heather Watson also appear in the film, raising their hands.
Tiafoe says he was very certain of his feelings, but in two minds whether to speak out publicly.
“It’s a fine line, you’d have to say. I was 50-50 with getting it out, but I’m happy I did it in the end. There was definitely a tug of war, but sometimes it’s bigger than that, which this case was,” he said.
“You see all the riots going through the United States. It needed to be said. The way things are going right now we definitely need change.”
He was ultimately persuaded by his girlfriend that a collective statement was the right thing to do.
“I think it was important to portray the power that black tennis players have,” Ayan said.
“I think that a lot of the time we forget how much we can accomplish when we come together. We were amazed that Serena, Naomi, Coco, Sloane, Monfils were so open to stand with us.
“Everyone has really big platforms, so the fact that we are able to share it on such a wide level was incredible.”
Osaka and Gauff have also made their feelings clear in other ways.
Osaka, a two-time Grand Slam champion, posted a photo of herself apparently among protestors in Minneapolis and another of the memorial to Floyd.
Gauff, who is just 16, appeared on TikTok wearing a black hoodie as the names and photos of African-Americans killed by police are revealed on the screen.
