A man died after being hit in the head by a skateboard outside of a Santa Ana, Calif. Starbucks store, leaving police trying to determine whether the killing was an act of self-defense or aggravated assault.

Officers were called to Starbucks at around 12:30 p.m. Tuesday, where they were notified that a man in his 50s walked into the store and approached a man in his 20s. The two eventually got into a verbal argument, police said, which led to a physical altercation, according to The Los Angeles Times.

The younger man reportedly hit the older man in the head during the fight, police said. After being struck, he went into cardiac arrest, prompting him to be taken to the hospital where he was pronounced dead.

Several witnesses claim that the older man had been acting erratically -- bothering customers and punching store windows, KTLA reported.

"He just came abruptly into the store, looked at the kid, and said, 'Did I stutter?'" witness Jocelyn Martinez said. "He took at step forward towards the kid as if he were going to attack him, and that's when the kid hit him with the skateboard."

"He did what anybody, I guess, would do when they feel attacked. They're going to protect themselves," Martinez concluded.

The younger man remained at the scene where he was questioned by detectives from the nearby station, according to ABC's California affiliate KABC-TV.

The Starbucks was closed during the investigation.