Jesse Vieira either callously smashed a security guard in the head with his skateboard and fists, leaving the man with a fractured skull and severe brain injury, or he was defending himself when the guard charged at him in a clash last year in San Francisco’s Financial District.

Attorneys in the case sparred over what the multiple videos of the encounter showed in the two-week trial that came to a close on Wednesday, leaving the San Francisco Superior Court jury to deliberate the fate of the 24-year-old defendant.

Vieira — a star skateboarder originally from Stockton — is charged with assault with a deadly weapon, assault with force likely to commit great bodily injury and battery with serious bodily injury in the Nov. 25 run-in that left Dan Jansen, 57, with a crater in his head that will forever impede his basic functioning.

The altercation happened as Jansen set up barricades around 555 California Street, a plaza at the foot of the 52-story skyscraper that once housed Bank of America’s headquarters. The place is known to skaters as Black Rock. Vieira and six other men were skateboarding at the plaza that day, some moving the metal barriers, before things escalated and ended with Jansen striking the back of his head on the hard granite paving.

Assistant District Attorney Blair Pickus compared the skateboarders to “a swarm of bees or a pack of wolves” who, he said, instigated things. Jansen was shoved to the ground by another skater moments before Vieira hurled Jansen’s radio at him, prosecutors said.

The security guard then got up and moved toward Vieira, who landed the devastating blows and left Jansen unconscious, prosecutors said. The seven men then took off.

“Entitled, self-important, disrespectful,” Pickus said in his closing argument. “Putting his own personal gain above the safety and well-being of Dan Jansen. That was the defendant Jesse Vieira. When literally push came to shove, it was the defendant who turned to his old trusty skateboard to get out of the situation.”

Vieira’s attorney, Doug Rappaport, argued that his client hit Jansen only after the security guard charged him. Rappaport played a video recorded by one of the young men in the group that he said shows Jansen striking Vieira first.

“Dan Jansen lost his cool that day,” Rappaport said in his closing. “He saw red and he went after the smallest guy in the group. He was pissed, adrenaline was flowing through his body. He clocked him good, and we have it on video.”

What’s more, Vieira was simply spiking Jansen’s radio on the ground, not throwing it at him, Rappaport said. And before Jansen got up, Vieira was walking away, he said.

“He’s not an angel, but that doesn’t mean he’s committed a crime,” Rappaport said, adding that his client had no criminal record.

Police arrested Vieira after executing a search warrant at his home on Dec. 10. He sat quietly in court Wednesday, wearing a dark blue sweater and collared shirt.

The case has drawn wide attention in the skateboarding community in the Bay Area and beyond. Vieira is a member of the well-known GX1000 crew that gained fame for its daring hill bombs and breathtaking tricks on the streets of San Francisco. He’s listed as a team member for Pizza skateboard company and was featured on the August cover of Thrasher magazine, grinding down a staircase railing at the Powell BART Station.

Around 30 fellow skateboarders and friends have packed the courtroom gallery every day of the trial and each previous court hearing, while Vieira remains in custody in San Francisco Jail. Vieira’s supporters declined to speak with The Chronicle after court.

Last week, fellow GX1000 crew member Pablo Ramirez, known as Pspliff to his friends and on social media, was struck and killed while hanging onto a dump truck — “skitching” as it’s called — after leaving the trial for the afternoon recess on April 23. His death devastated the group, who cried and embraced each other as they learned of the tragedy and gathered at the scene four blocks from the courthouse.

Vieira’s friends this week watched intently as attorneys laid out their arguments in the case. Most of the evidence came in the form of four videos that showed different angles of the run-in — including the key video shot by the skateboarder. The attorneys also played police body-camera footage and 911 calls, and called various witnesses before questioning Vieira himself on the witness stand.

As the case has progressed in court, Jansen has been going through a slow and agonizing recovery. Doctors put him into a medically induced coma after he suffered a spiderweb-type fracture in the back of his skull and bleeding in the brain.

Surgeons removed part of his skull and frontal lobe in order to cauterize a wound in his brain and save his life. He’s since undergone two more brain surgeries and after recovering slightly, he’s begun to regress, his niece, Amanda Jansen, said.

Dan Jansen still can’t walk and is just starting to recognize some family members who visit him at an assisted living facility where he has live-in care. A former soldier in the Army and avid fisherman, Jansen faces a long road ahead. It’s not clear if he will be able to care for himself ever again, his family said.

“The impact of this is devastating,” Amanda Jansen said. “It’s really hard. My uncle’s life as he knew it is over.”

Evan Sernoffsky is a San Francisco Chronicle staff writer. Email: esernoffsky@sfchronicle.com Twitter: @EvanSernoffsky