They began filing into the two ballparks at close to the same time, descending their respective subway platforms, easing their cars into parking lots.

This was late in the afternoon of Aug. 18, 1983. In those years, Yankee Stadium and Shea Stadium rarely had days where both were in use. The rhythms of the baseball season meant that when the Yankees were in town, the Mets were in Philly or Pittsburgh or Cincinnati; when the Mets were at Shea, the Yankees were off in Boston or Detroit or Cleveland.

And if they ever did share a home date in those years?

Well, it wasn’t close. The Yankees drew over 2 million fans every full year from 1976 through 1983, the Mets never more than 1.4, and the past four full years that number had barely averaged a million. But this was a different kind of day.

In The Bronx, where something resembling a miniature baseball game was scheduled to start at 6:05 p.m., there was barely a trickle of fans and whatever traffic was clogging the Deegan was bound 10 miles farther south, in Queens. The Yankees and Royals would be resuming the Pine Tar Game. Fans who held ticket stubs from that game, which began on July 24, would be admitted free. For anyone else, it was $2.50.

Officially, 1,250 people showed up.

Unofficially?

“Five hundred? I say 500,” Don Mattingly said afterward, when Dan Quisenberry had set the Yankees down 1-2-3 on 10 pitches to end the game 5-4.

“More like 250,” said Ron Guidry.

At that very moment, there were already close to 50,000 people in the stands at Shea, listening to an unknown band out of Athens, Ga., named R.E.M., the first warm-up act of a triple bill that would include Joan Jett and the Blackhearts and, close to 8:30 or so, The Police. By then, there were 70,000 people jammed into the joint, and they were soon greeted by the star of the night, a slight blond singer who was born Gordon Sumner.

“We’d like to thank the Beatles,” Sting said, “for lending us their stadium.”

The day started badly for the Yankees and it only got worse from there. They’d lost a gut-wrenching game against the White Sox in 13 innings, a game that leaked past midnight. Afterward, their ascendant young shortstop, slick-fielding Andre Robertson, met a friend from back home in Texas, a ballet dancer and law student named Shenikwa Nowlin.

The pair went to Studio 54, and as they left around 4 a.m. — neither had been drinking, nor using drugs — they hatched an idea to take the Staten Island Ferry to see the Statue of Liberty at dawn. Robertson drove them to his apartment in Fort Lee to pick up a camera, and then headed back into the city.

Shortly after 5 a.m., going around 70 mph in a 55-mph zone, Robertson failed to negotiate an “S” Turn on the West Side Highway around 72nd Street. He lost control of his Buick, slammed into a median and flipped over. Nowlin would be rendered paraplegic by the accident. Robertson broke his neck and hurt his shoulder, and while he recovered to play parts of two more seasons with the Yankees, his career would essentially be done at age 25.

The Yankees were stunned when they arrived at the Stadium midday, but the sadness of the Robertson crash was already overwhelmed by the silliness of the surrounding fury of business at hand.

In the morning, a State Supreme Court Judge named Orest Maresca had somehow kept a straight face while issuing an order to enjoin the game and saying, in part: “Yankee pinstripes are the end-all and be-all of young and sometimes old Yankees fans.” That took place in The Bronx. A few hours later in Manhattan, an Appellate Court Judge named Joseph Sullivan overturned that ruling, disappointing a number of lawyers who’d argued to keep the ban intact, including Roy Cohn.

The closing to Judge Sullivan’s ruling?

“Play ball!”

And so they did. The Royals took a bus from Newark Airport to the Stadium, but George Brett stayed on the team charter. One of the few things that hadn’t changed was that Brett was still ejected from the game after storming the dugout with murderous intent when ump Tim McClelland ruled him out for having too much pine tar on his bat after hitting a go-ahead homer off Goose Gossage with two outs in the top of the ninth back in July.

“I had nothing left to say,” Brett crowed with a laugh years later.

But AL president Lee MacPhail had upheld the Royals’ protest of the ruling, and so here the Royals were, back in New York on a shared off-day before heading to Baltimore. But even now there was more: Billy Martin jogged onto the field to claim Brett had missed first base on his home run trot, and started to do the same at second.

But MacPhail was way ahead of him. He’d already obtained a notarized statement from all four original umpires that Brett had, indeed, touched all four bases, and Martin was shown the note by umpire Dave Phillips. Martin’s response was to send Ron Guidry out to play center field — he needed someone; Jerry Mumphrey, who’d played July 24, had been traded to the Astros. George Frazier retired Hal McRae, and then Quisenberry made quick work of the Yankees. The 1,250 — or 500, or 250 — filed out quietly.

Maybe some of them even hopped on a train bound for Queens.

The concert had been announced in June, and within two hours all 70,000 tickets were sold, and it immediately became the most extravagant event in Shea Stadium’s history. When the Beatles had famously played there on Aug. 15, 1965, they kept the playing field free of fans, so that show maxed out at 55,000. Not so three days shy of 18 years later, and for much of the preliminary the thousands on the field made like human squeegies, sliding across the tarp in torrential downpours.

Those in the upper levels — including your humble narrator — had to make do being introduced to R.E.M., whose five-song set list included “Radio Free Europe,” which WLIR had just started playing, and “Catapult.” Jett and the Blackhearts were next, and their basement-rock style easily played to the swelling crowd who sang along with every note of “Crimson and Clover,” “Fake Friends” and “I Love Rock and Roll.”

Then Martha Quinn — the MTV DJ who 90 percent of teenage boys had a crush on in 1983 — took to the stage, endured a few whistles and catcalls, and introduced Andy Summers, Stewart Copeland and Sting. The 21-song set started off with “Synchronicity I,” ended with “So Lonely” and included every one of the songs the 70,000 in the house wanted to hear.

“Thank you, New York, we’ll be back!” Sting bellowed at the end, but of course they wouldn’t be. Police-ologists know that concert was the beginning of the end for one of the most combustible bands of all time. And the end of the end of one of the most remarkable days that pop-culture New York had ever seen.