A female singer performed the National Anthem while kneeling at midcourt before an NBA preseason game in Miami Friday night, opening her jacket to show a shirt with the phrase "Black Lives Matter."

The Miami Heat identified the singer as Denasia Lawrence. The team said of her gesture, "We were unaware of it ahead of time."

Lawrence posted video of her performance on Twitter along with a statement saying in part that "I took the opportunity to sing AND kneel; to show that we belong in this country AND that we have the right to respectfully protest injustices against us."

Heat players and coaches stood side-by-side for the anthem, all with their arms linked as has been their custom during the preseason. Many had their heads down as Lawrence sang before the game against the Philadelphia 76ers. 

The anthem issue has been a major topic in the sports world in recent months, starting with the decision by San Francisco 49ers quarterback Colin Kaepernick to not stand for its playing. Kaepernick cited racial injustice and police brutality among the reasons for his protest, and athletes from many sports — and many levels, from youth all the way to professional — have followed his lead in various ways.

"All I can say is what we've seen in multiple preseason games so far is our players standing for the national anthem," NBA Commissioner Adam Silver said in New York earlier Friday, at a news conference following the league's board of governors meetings. "It would be my hope that they would continue to stand for the national anthem. I think that is the appropriate thing to do."

The NBA has a rule calling for players and coaches to stand during the anthem.

Making a statement in the manner that Lawrence did Friday is rare, but not unheard of in recent weeks.

When the Sacramento Kings played their first home preseason game earlier this month, anthem singer Leah Tysse dropped to one knee as she finished singing the song.

Tysse is white. Lawrence is black.

"I love and honor my country as deeply as anyone yet it is my responsibility as an American to speak up against injustice as it affects my fellow Americans," Tysse wrote on Facebook. "I have sung the anthem before but this time taking a knee felt like the most patriotic thing I could do. I cannot idly stand by as black people are unlawfully profiled, harassed and killed by our law enforcement over and over and without a drop of accountability."

The Associated Press contributed to this report.