The video shows Marvin Norwood sitting in an interrogation room, speaking to his mother on an LAPD detective’s cellphone.

“Hey, I got arrested for that Dodger Stadium thing,” the 31-year-old says. “I was involved.... To a certain extent I was.”

He tells his mother he can’t say much over the phone but says Louie Sanchez, 30, is also in custody.

Norwood then apologizes: “Pretty sure I’m going down for it.... I’m sorry.”

The video was the first piece of evidence Los Angeles County prosecutors put forth Wednesday during the opening day of the preliminary hearing for Norwood and Sanchez. The hearing will determine whether there is enough evidence for the two men to stand trial on charges of mayhem, assault and battery, and inflicting great bodily injury in the brutal beating of San Francisco Giants fan Bryan Stow at Dodger Stadium on opening day last year. Stow, a 43-year-old father of two, suffered serious head trauma and remains in a therapeutic facility.

The incident drew national attention and calls for police, city officials and the Dodgers to tighten stadium security and better protect fans.

Flanked by their attorneys, the defendants — who changed from blue, jail-issued jumpsuits to dress clothes during a lunch break — sat as seven witnesses testified that Sanchez was rowdy and inebriated during the March 31, 2011, game. Sanchez attended the opener with his sister, his 11-year-old son and Norwood, a friend and neighbor from Rialto.

Early in the game, witnesses said, Sanchez began throwing peanuts and yelling obscenities at a couple wearing Giants attire who were sitting across the aisle. He laughed as he did so and even got his son to throw a few peanuts, said Geraldine Carrasco-Burg, who was sitting behind the group.

The heckling stepped up a notch, she said, around the seventh inning, when Sanchez asked Carrasco-Burg and her husband if they “would be mad” if he threw soda on the Giants fans. Sanchez spent the remainder of the game repeating the question and looking for something to throw, she said.

“I said, ‘That’s not right, no, that’s not nice,’” Carrasco-Burg recalled.

But shortly after the last pitch, Sanchez grabbed a soda bottle, shook it and sprayed the liquid on Kathryn Gillespie and her boyfriend, Griffith McDaniel.

McDaniel put his hands up and moved toward the center aisle. Sanchez, witnesses said, looked “ready to fight.”

Gillespie began pushing her boyfriend back as Norwood grabbed Sanchez, she said. McDaniel said he and Sanchez stared at each other for “about 30 seconds,” but no physical confrontation occurred.

Instead, other fans ushered the couple away from Sanchez and Norwood. Carlos Adane was one of them.

“They were just thugs,” he said of Sanchez and Norwood. “They were looking for trouble.”

The witness testimony backed previous filings by prosecutors in which they alleged that the defendants were aggressive throughout the game and pushed another fan as they walked out of the stadium into the parking lot, where they ran into Stow.

Police initially arrested parolee Giovanni Ramirez for the crime but could not link him to the beating. The case was reassigned to robbery-homicide detectives, who re-interviewed witnesses and reexamined security video, which led to the July 21 arrests of Sanchez and Norwood.

Already facing charges of felony assault and mayhem, the pair were indicted earlier this month on federal charges of being a felon in possession of a firearm. Authorities said the latest charges stem from guns and ammunition found at Sanchez’s home during searches executed before his and Norwood’s arrests.

The preliminary hearing continues Thursday before Los Angeles County Superior Court Judge George G. Lomeli. It is expected to last up to four days.

kate.mather@latimes.com