A hot-headed old-timer turned his Long Island “Super Senior” softball league into a field of screams by threatening to beat his teammate/manager’s “brains out” with a bat — and even to stalk him at his neighborhood pharmacy, a new lawsuit charges.

The diamond dust-up broke out after Ronald Tagliaferri, 74, of Shoreham, and Robert Willis, 72, of Ridge, got into a squabble over the color and cut of uniforms for their team, the Kingsmen, in March 2013, according to the Suffolk County filing.

Tagliaferri, an outfielder who had previously been manager, stormed Willis, a third baseman who replaced him running the squad, with his fists clenched, forcing teammates to jump in, according to the lawsuit.

Things got so heated, the suit states, that Tagliaferri, “in a menacing and threatening tone,” later left a message on Willis’ voicemail telling him he knows where he “gets his prescriptions filled” and that Willis “should be on the lookout.”

Spooked, Willis switched to a different team, the Eagles.

But Tagliaferri — who is so obsessed with softball that his license plate reads “0 Errors” — maintained a grudge, according to the suit.

Three months later, he called Willis, threatening to “beat [his] brains out with a baseball bat” if he showed up for a game, the suit says.

It came to a head when the Eagles faced the Kingsmen in August.

The umpire called Willis out at second base, but the hard-of-hearing baserunner asked him to repeat the call — and Tagliaferri exploded, the lawsuit states.

“Hey, you’re out! Get off the goddamn base!” he shouted, the suit says. Tagliaferri charged at Willis and again had to be restrained, the suit states.

Tagliaferri called the allegations “outright lies.”

“I never threatened him with a bat . . . He has osteoporosis. He doesn’t walk too great. I wouldn’t do anything to [hurt] this guy,” said Tagliaferri, who said he retired from the NYPD after 25 years patrolling in Brooklyn. “I never heard of anyone taking someone to court over an argument on the baseball field.”

“Mr. Willis has loved and played this game his entire life,” said his attorney, Vesselin Mitev of the firm Ray, Mitev and Associates.