At the heart of the government's case is a surveillance video that shows Mr Combs beating Ms Ventura and dragging her by the hair in a Los Angeles hotel hallway in 2016.
Lawyers for Mr Combs said the video was evidence of Mr Combs' "flawed" character, but not of a larger criminal enterprise. "Domestic violence is not sex trafficking," said Teny Geragos, Mr Combs' attorney.
Ms Geragos said Mr Combs has a "bit of a different sex life" - and shifted the focus to the women accusing him, calling them "capable, strong women" who chose to stay with the rapper.
They had "the freedom to make the choices that they made", Ms Geragos argued.
Prosecutors' first witness, a former security guard named Israel Florez, worked at the hotel, the site of a surveillance video showing Mr Combs attacking his ex-girlfriend. The clip, which CNN released last year, was played for jurors on Monday.
Mr Florez told jurors that morning on 5 March 2016 at the InterContinental Hotel in Los Angeles he received a call about a "woman in distress" on the sixth floor.
He said he found Mr Combs there in a towel, slouched on a chair with a "devilish" look on his face, and a broken vase on the floor. Ms Ventura sat cowering in the corner with her face covered, Mr Florez said.
Mr Florez told prosecutors that Ms Ventura kept saying she wanted to leave, but Mr Combs told her she could not.
He testified that Ms Ventura had a purple eye, but did not want to call police and she eventually left in a black SUV.
Mr Florez alleged that later, to "make it go away", Mr Combs tried to hand him a wad of cash, but he declined.
Attorneys for Mr Combs tried to poke holes in Mr Florez's claims, asking why he did not include certain details - like Ms Ventura's purple eye - in an incident report he filed afterwards.