A suburban Pittsburgh youth football league says it is investigating reports of racial slurs being hurled at an all-black team after some took a knee during the national anthem.

Woodland Hills head coach Marcus Burkley tells WPXI-TV his team was playing Bethel Park on Saturday when two or three of his 12- and 13-year-old players took a knee. He says that's when the racial slurs started coming from the stands. Some of his players told him kids on the mostly white opposing team also used the slur.

He says police were eventually called as tensions mounted.

The president of the Bethel Park Junior Football League says it's investigating.

San Francisco 49ers quarterback Colin Kaepernick has been widely criticized for his similar form of protest. He cites racial injustice.