Bobby Thomson of the New York Giants hits a home run off Mr. Branca in a playoff game at the Polo Grounds in New York on Oct. 3, 1951. (AP)

If not for one unforgettable fastball, hurled Oct. 3, 1951, pitcher Ralph Branca of the Brooklyn Dodgers might have faded from baseball memory. In a dozen major league seasons, he won 88 games and lost 68, a workmanlike record, a ticket to obscurity.

But for an autumn afternoon long ago.

Facing the New York Giants with a 4-2 lead and the National League championship at stake, he threw a high fastball in the ninth inning to the Giants’ Bobby Thomson, a dangerous hitter.

And Thomson hit history’s most legendary home run, a game-ending, pennant-clinching, bedlam-inducing (and since controversial) rocket into the left-field stands at New York’s old Polo Grounds, a three-run blast that lives in lore as “the shot heard round the world.”

The two teams, blood enemies, had been tied atop the standings on the season’s last day. After the riotous joy unleashed in their Harlem ballpark, the Giants moved on to the World Series, while the luckless losing pitcher, No. 13 of the Dodgers, was cast into sports ignominy, maligned as an all-time goat.

Bobby Thomson, left, and Mr. Branca before a World Series game at Yankee Stadium in 1951. (AP)

Mr. Branca, who had been summoned from the bullpen to quell a ninth-inning rally, and who bore the burden of his failure with quiet dignity for decades, died Nov. 23 at a nursing home in Rye Brook, N.Y. He was 90. His daughter Patti Branca confirmed the death and said she did not know the cause.

In Mr. Branca’s time with the Dodgers, “Dem Bums” of the early postwar era, at once maddening and beloved, were good yet never quite good enough. After the loss, as grief consumed the denizens of Brooklyn, Mr. Branca, then 25, endured catcalls and death threats. Photographers and sports writers pestered him, milking his anguish, and disconsolate cranks harassed his parents.

Still, until late in life, he seldom griped about his fate, despite knowing that his crosstown foes were guilty of elaborate chicanery. For weeks in 1951, it was later revealed, the Giants had been able to decipher and take advantage of opposing teams’ on-field signs, using a covert system of electrical buzzers, buried wires, cryptic gestures and, most important, a powerful telescope mounted high in their cavernous stadium.

In the latter half of the season, when Giants hitters were at bat in the Polo Grounds, they were often tipped seconds in advance about whether a fastball or an off-speed pitch was coming, and they adjusted their swings accordingly.

Mr. Branca, who was released by the Dodgers in 1953 and joined the Detroit Tigers, said he learned of the skulduggery from one of his new teammates.

“For years, I struggled with anger and resentment,” he recalled in his 2011 autobiography, “A Moment in Time: An American Story of Baseball, Heartbreak, and Grace,” written with David Ritz. “I was advised to capi­tal­ize on and expose the scheme. Go to the press. . . . Do something. But I refused. I didn’t want to be seen as a whiner, a sore loser, or a baby crying over spilt milk.

“Take it on the chin. Accept the blow. Move on with your life. Or, best of all, forget about it, which proved impossible.”

Journalist Joshua Prager documented the long-rumored pitch-tipping in a 2001 Wall Street Journal article and in his 2006 book “The Echoing Green: The Untold Story of Bobby Thomson, Ralph Branca and the Shot Heard Round the World.”

Although sign-stealing is an ancient baseball art, and the rule book in 1951 didn’t explicitly forbid using mechanical devices (as it does now), the Giants’ systematic spying violated an unwritten code. Only a half-century later, speaking with Prager, did many of the ’51 veterans, including Thomson, sheepishly acknowledge what they had done.

And only after that did Mr. Branca begin talking about it publicly.

Thomson, who died in 2010, insisted that his historic home run was legitimate, that during his final at-bat on Oct. 3, 1951, he neglected to glance at the Giants teammate who was relaying pitch intelligence. But Mr. Branca, who became unlikely close friends and memorabilia-signing partners with Thomson in their elder years, said in his memoir, “I didn’t believe him.”

The scheme, the brainchild of pugnacious Giants Manager Leo Durocher, had been hatched weeks earlier, on July 19, with the Giants buried in the standings. It continued through an epic late-season comeback dubbed “the Miracle of Coogan’s Bluff,” for a plateau overlooking the Polo Grounds.

By Sept. 30, after a 49-17 turnaround, the Giants had climbed from a low of 131/2 games behind Brooklyn to a first-place tie. Winning consistently at home seemed to relax the players on the road, where they also won at a torrid pace. The Dodgers, 23-18 down the stretch, wound up in a best-of-three playoff for the National League title.

Baseball owned America back then. The Dodgers and Giants were the sport’s fiercest rivals, and their series was the first to be televised coast to coast.

Mr. Branca, the opening-game starter, gave up a fourth-inning homer to Thomson and lost a pitchers’ duel. Brooklyn prevailed the next day in a rout, forcing Game 3. In the bottom of the ninth, with runners on second and third and Thomson due up, Mr. Branca came in from the bullpen to preserve a 4-2 lead. He needed to get two outs.

Mr. Branca, a three-time all-star in the late 1940s and a 21-game winner in 1947, was no stranger to pitching in relief. The 6-foot-3, 220-pound right-hander made 27 starts and 15 relief appearances in 1951, finishing with a 13-12 record and a solid 3.26 earned-run average, before injuries took a toll and his career went down hill.

His second pitch to Thomson was up and in — just not up and in enough — and the Giants third baseman hammered it. “There’s a long drive!” play-by-play announcer Russ Hodges famously bellowed, channeling the home crowd’s sudden euphoria. “It’s gonna be — I believe!” The ball, its whereabouts a mystery ever since, found the seats above the 315-foot sign on the high left-field wall.

Pandemonium ensued — baseball’s first big theatrical moment on national TV — with Thomson dancing around the bases; fans storming the field as Mr. Branca and the Dodgers trudged off; and Hodges shouting over and over, “The Giants win the pennant!”

A defining photo shows Mr. Branca in tears, sprawled face down on steps in the visitors’ clubhouse. Consigned to the gallery of eternal goats, he would soon be hanged in effigy, his No. 13 dangling from Brooklyn lampposts.

“I wanted to believe that I was dreaming,” he wrote. “I didn’t want to believe that it was really happening. I wanted the pitch back.

“But the ball was gone and the game was over.”

Ralph Theodore Joseph Branca, the 15th of 17 siblings, was born Jan. 6, 1926, in Mount Vernon, N.Y., 25 miles from Ebbets Field, the Dodgers’ old Brooklyn home. His father, an Italian immigrant, worked variously as a barber, plumber, mechanic, house painter and trolley conductor.

At age 85, the devoutly Catholic Mr. Branca learned that his late mother had been Jewish at birth in her native Hungary. The discovery was made by Prager, who found out that at least nine of Mr. Branca’s aunts, uncles and cousins had perished in Nazi death camps.

A schoolboy athletic star, Mr. Branca signed with the Dodgers in 1943, when he was 17, and made his major league debut a year later. After a decade with Brooklyn and stints with the Tigers and New York Yankees, he left baseball in 1956 and spent the rest of his working life in the insurance industry.

For 17 years starting in the 1980s, he also was president and chief executive of the nonprofit Baseball Assistance Team, providing financial help to former ballplayers who are down on their luck.

As for the ’51 Giants, it was never much consolation to him that they fell short in the World Series, losing to the Yankees in six games.

Survivors include his wife of 65 years, the former Ann Mulvey of Rye, N.Y.; two daughters, Patti Branca of Fort Myers, Fla., and Mary Branca Valentine, who is married to former major league manager and broadcast commentator Bobby Valentine, of Redding, Conn.; and three grandsons.

In 1947, when Jackie Robinson broke baseball’s racial barrier with the Dodgers, Mr. Branca, unlike others on the team, tried to make him feel welcome. Robinson would remember the ill-starred pitcher as among the handful of players he was most fond of, and, in 1972, Mr. Branca was one of Robinson’s pallbearers.

So it was that in the agony of the playoff loss, as Mr. Branca sobbed on the clubhouse steps, “hiding my face in shame,” a hand reached out.

“My teammates thought it best to leave me alone,” he recalled. “We were all shellshocked. Only my dear friend Jackie, who knew me so well, came over and put his arm around my shoulder. ‘Ralph,’ he said, ‘try not to take it personally. If it weren’t for you, we would have never made it this far.’ ”