He went off the deep end.

A private security guard for Phish allegedly attacked a stadium worker at one of the band’s NYC concerts, the victim claimed in a lawsuit.

US Army veteran David Hone was getting ready to join the rest of the venue’s crew to break down the set at the end of the iconic jam band’s July 22 show at Forest Hills Stadium when Knute Brye charged at him, he said in a lawsuit.

Brye had been speaking with Hone’s supervisor but, “I couldn’t even make out what they were saying . . . the music and noise were so loud.”

Brye, 59, then began screaming at Hone, 35, and tried to put him in a headlock, he claimed in Manhattan Supreme Court papers.

“I saw Knute yelling, ‘Go, go, go’ . . . then I realize he’s looking at me, and walks up to me and all I hear is, ‘I’m sick of thi sh-t,'” he told The Post.

“I was like, ‘Whoah, whoah!’ and before I even know what’s going on, this guy who is twice my size, 6-foot-something and 200 something pounds — I’m 5-foot-9, 170-pounds — he reached for my lanyard and tries to pull it off my neck, pulling me forward.”

Brye scratched him and ultimately put him in a headlock, Hone alleged, aggravating preexisting shoulder problems.

“I finally was able to place my hands on his chest and push off of him and put my finger in his face and say, ‘Keep your hands off of me, I work here.'”

Hone, who got the job just four months earlier thanks to a US Department of Veterans Affairs vocational program, claimed he was later wrongly fired for “insubordination.”

The NYU grad is suing Brye and Phish for negligence and unspecified damages.

Brye and a rep for Phish did not return a message seeking comment.