An American Airlines passenger was detained by the FBI after being caught on a cellphone video punching a flight attendant in the head aboard a flight from Mexico to Los Angeles.

The airline said in a statement that the assault took place on Flight 377 from San Jose del Cabo to LAX on Wednesday, reported CBS News.

According to the feds, the passenger was removed from the plane after it touched down in Los Angles and was detained on suspicion of interfering with a flight crew — a federal felony punishable by up to 20 years in prison. The suspect has not been named.

A 30-second recording made by fellow passenger Barrie Livingstone, which has been shared on social media, shows a male flight attendant standing in the middle of the aisle and asking a passenger, “Are you threatening me?”

The crew member then turns his back on the unruly passenger, dressed in an orange floral shirt, who runs up to the American Airlines employee from behind and strikes him in the back of the head with a closed fist.

“Oh, my God!” another traveler exclaims. “What are you doing?”

A producer for KFMB-TV, Malik Earnest, who was on the flight, said other passengers restrained the assault suspect until he was removed by cops.

Another passenger told ABC Eyewitness News that the flight attendant did not appear to be seriously hurt.

The witness, who gave his name only as Kevin, confirmed that the suspect was restrained by other passengers using zip ties.

Kevin also claimed that prior to the alleged assault, the suspect began to whisper that “there are 10 killers on the plane.”

According to the witness, a female flight attendant made the man sit down, before her male colleague went over and confronted him.

American Airlines said in its statement that the out-of-control passenger “will never be allowed to travel with us in the future.”