It is the walkoff home run of live action sports shots. Carlton Fisk is waving the ball fair. He’s perfectly in focus, perfectly framed slightly to the right as he drifts left toward first base. As the ball hits the fair pole, he jumps, Fred Lynn in the on-deck circle behind him jumps, and the dozens of fans in the shot behind him jump.

It is one of the most famous and enduring images in American sports history. More important than that, it forever changed the way television covers baseball.

And it almost never happened.

The story behind it is one of the great—and little-known—tales in Fenway Park’s 100-year history.

In 1975, cameramen did not follow players’ reactions. They followed the ball. Reaction shots like that one, so ubiquitous today, were largely unheard of. Then Fisk, the Red Sox catcher, stepped to the plate in the 12th inning of Game 6 of the World Series. NBC cameraman Lou Gerard, stationed in the Fenway scoreboard and assigned to track the ball wherever Fisk hit it, had a problem.

A big, hairy, ugly, nasty problem.

“There were some rats running around,” he says. “With Fisk coming up, Harry Coyle, who was the director at the time, he told me, ‘Lou, you have to follow the ball if he hits it.’ I said, ‘Harry, I can’t, I’ve got a rat on my leg that’s as big as a cat. It’s staring me in the face. I’m blocked by a piece of metal on my right.’ So he said, ‘What are we going to do?’ I said, ‘How about if we stay with Fisk, see what happens?’ ”

Coyle already was a pioneer in how TV covered baseball, unafraid to try new things. It was his idea to put a camera in center field—which became the view of virtually every pitch. Coyle, who died in 1996, said in the book “Voices of the Game” that he got that idea from watching an umpire in a softball game call balls and strikes from behind the pitcher. Coyle was the type of guy who would go along with Gerard’s plan.

“Harry says, ‘OK, we’ll try that,’” Gerard says.

With those four words, Coyle and Gerard introduced a new way of televising America’s pastime.

Fisk’s reaction was emotional, real, unforgettable. There were only three networks then, and after a series of rain delays that led to a ton of hype, there was a lot of anticipation for the game. When the game provided an unforgettable ending, TV captured it in an unforgettable way.

“It was after that Fisk shot, that had so much attention, that now you started seeing more cameras brought to big events that would actually focus on those emotional moments as they unfolded,” says David Gavant, the executive in charge of production and executive producer of Major League Baseball Productions.

At the time, Gerard just thought it was a nice shot of a great moment.

Inside the production truck, producer Roy Hammerman thought the same thing. NBC did not use Gerard’s shot live. The live shot followed the ball as it soared into the night, plunked into the fair pole and fell at the feet of Reds left fielder George Foster. As that happened, Hammerman was watching the monitors. Looking at the screen showing Gerard’s shot, he saw TV gold.

“I told the guys, ‘Get ready for the replay,’ ” Hammerman says.

They did. Again and again. In his 19-year career, Hammerman was nominated for 16 Emmys and won once, for the 1975 World Series, for decisions like that one.

“We replayed it about 12 times,” says Hammerman, who is now retired and lives in California.

Thirty-six and a half years later, it feels like 12 million. It is one of the most replayed highlights in any sport, and arguably the most important in terms of the way baseball is broadcast now. Gerard’s shot had a bigger impact than the home run itself; the Red Sox lost the World Series in Game 7. But the change in TV that followed endures, from Kirk Gibson pumping his fist after his walkoff in Game 1 of the 1988 World Series to Joe Carter’s jubilant tromp after his World Series-winning home run in 1993 to every player who pimps it on the way to first.

That home run is the defining moment of Fisk’s Hall of Fame career. Within the sports TV industry, Gerard is famous for his work that night, too. He was part of an answer on “Jeopardy!” Bring up his name among his contemporaries, and they know who he is and what he did. Gerard got a kick when he was watching TV recently and his old friend Bob Costas name-dropped him.

“Louie had the greatest shot of all,” says Lenny Basile, who worked a center-field camera that night in Boston. “It was just fantastic.” Basile and others who know Gerard say it couldn’t have happened to a nicer guy. Gerard will turn 85 in August. He has two children, two grandchildren and one great-granddaughter. He retired in 1986 with four Emmys on his shelf and lives on Long Island with his daughter, Julie Hartley.

He began his TV career in 1951—before color, before cameras could move, before coast-to-coast connections. He started out making $29 a week after leaving an engineering job he didn’t like for which he was making $32. But he never regretted it. He loved his career behind the camera for just about every major sporting event there is.

“There was never a dull day. I enjoyed it immensely, all the time I worked there,” he says.

He’s proud of the shot. So is Hartley. She kept a scrapbook of stories about it. When people ask about those Emmys on the shelf, she delights to tell them. She loves the story about the rat—it wasn’t the only time he encountered a furry, uninvited guest. “That drove my mother crazy—‘Don’t get bit by rats!’ ”

He didn’t know then he’d still be talking about Carlton Fisk now. Though there were some hints. As he was leaving the Fenway that night, the executive producer, Scotty Connal, who later helped start ESPN, called out to him from the production truck.

“He said, ‘Louie, come in here, I want to show you something.’ He said, ‘Do you know what you’ve got here?’ I said, ‘Yeah, I got Fisk waving his arms, trying to keep the ball fair.’ He said, ‘Yeah, but we’ve never done that before. That’s going to change what we’re going to have to do every time we take a shot.’ He says, ‘You changed television.’ That’s what he said to me.”

That poor rat got no credit at all.