“Uyaya ejele…uyaya uOscar uyaya…” they sang.
The song says “Oscar is going to jail”. The ANCWL were joined by men in civilian clothes.
The trial was delayed as the court waited for an Afrikaans interpreter.
Pistorius, 27, is charged with murdering his girlfriend Reeva Steenkamp at his home in Pretoria on Valentine’s Day last year and contravening the Firearms Control Act.
He has said he thought she was an intruder when he shot her through a closed toilet door.
The proceedings in the wood-panelled courtroom will be broadcast live on television and radio, with the initial indictment listing 107 witnesses to testify for the State.