Ventura, an R&B singer known as Cassie, testified on Tuesday she acceded to taking part for a decade in Combs' drug-fuelled parties known as "Freak Offs", often fearful he could become violent if she did not.
Jurors saw a 2016 surveillance video from the hallway of a Los Angeles hotel where a towel-clad Combs threw Ventura to the ground and began to kick her.
She said the video was taken after a "Freak Off" where Combs gave her a black eye.
"I made it to the elevators, I got my sneakers on, and the next thing I knew, I was thrown to the ground," Ventura said.
Asked by a prosecutor why she stayed on the ground, Ventura said: "I felt like it was the safest place to be."
Ventura is the star prosecution witness at Combs' trial in Manhattan federal court.
Combs, 55, has pleaded not guilty to five felony counts of racketeering conspiracy, sex trafficking and transportation to engage in prostitution.
If convicted on all counts, he would face a minimum of 15 years in prison, and could face life behind bars.
The trial could last two months, and Combs is being jailed in Brooklyn when not in court.
Combs also faces dozens of civil lawsuits by women and men who accuse him of sexual abuse.
He has denied wrongdoing, and said his relationships were consensual.
Ventura, 38, testified that she once viewed her relationship with Combs, which began in her early 20s, as her first real adult relationship.
But she said Combs became more controlling as the "Freak Offs", which she said lasted as long as four days, took over their relationship and derailed her music career.
Combs has apologised for the video, and his lawyers have said prosecutors have tried to improperly punish him for his "swingers" lifestyle.
They are expected to cross-examine Ventura after she finishes her direct testimony.
Also known during his career as Puff Daddy and P Diddy, Combs founded Bad Boy Records and is credited with helping turn artists like Mary J Blige, Faith Evans, Notorious B.I.G. and Usher into stars in the 1990s and 2000s.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
