A man watching “The Shallows” was stabbed on Wednesday afternoon at the Roxy Theater in downtown Santa Rosa, Calif., Variety has confirmed.

The 21-year-old male was attacked from behind around 4 p.m. — 30 minutes into the movie — and stabbed numerous times before running out of the theater though the lobby, according to Santa Rosa police. The victim suffered life-threatening injuries and remains hospitalized.

“Out of nowhere, he came up from behind him, he stabbed him in the throat, in the arm, in the lung,” Santa Rosa Police Sgt. Josh Ludtke told the Santa Rosa Press Democrat.

Police shut the second floor of the two-story theater to collect evidence on Wednesday night.

An unidentified 23-year-old man was arrested on suspicion of attempted murder. Police, who recovered the weapon from a trash can outside the auditorium, said the attack appears to be random and unprovoked.

Ludtke told the Press Democrat that the suspect may be tied to another homicide: A man was stabbed 50 times on Monday morning in downtown Santa Rosa.

“Based on the randomness of the act, the brutality of the act, certainly he’s a person we’re looking into as a suspect,” Ludtke said.

“The Shallows” — a shark thriller starring Blake Lively — opened in theaters last weekend to $16.8 million.