As the second week of Sean Combs’s racketeering conspiracy and sex-trafficking trial begins, the first witness is set to be Dawn Richard, a singer in two music groups backed by Mr. Combs who says she saw him physically abuse his former girlfriend, Casandra Ventura.

A performer in the now-defunct groups Danity Kane and Diddy — Dirty Money, Ms. Richard began her testimony on Friday, recalling an incident from 2009 in which she said Mr. Combs attempted to hit Ms. Ventura, known as the singer Cassie, with a skillet, then punched and kicked her.

“She went into fetal position — you could see she was literally trying to hide her face or her head,” Ms. Richard testified. She also said that Mr. Combs threatened her and a bandmate to keep silent about the event, saying he told them that “where he comes from, people go missing if they say things like that, if they talk.”

Ms. Richard filed a lawsuit against Mr. Combs last year, shortly before he was arrested. She accused him in the suit of threatening her, groping her and flying into “frenzied, unpredictable rages” while he oversaw her career. The girl group Danity Kane was formed during the third iteration of Mr. Combs’s MTV reality show “Making the Band.”

After the jury had been dismissed on Friday, a lawyer for Mr. Combs called Ms. Richard’s accusation of abuse from 2009 a “drop-dead lie,” noting that Ms. Ventura had not mentioned it during her four days on the witness stand.

Ms. Richard is the first of a series of government witnesses scheduled for this week who are expected to testify about what they saw of Ms. Ventura’s 11-year on-and-off relationship with Mr. Combs.