“There are so few things in the world that you can stand up and scream from the rooftops and not care what anyone says, because you know there’s absolute right and absolute wrong,” says Sean Astin, who played Rudy Ruettiger in the quintessential underdog movie, “Rudy.”

“And it is an absolute right and an absolute truth that this score by Jerry Goldsmith is perfect. It’s a perfect score.”

Goldsmith’s music, a glorious paean to the unflagging heart, will be celebrated Saturday in a live performance accompanying a 25th anniversary screening of the 1993 film at the Microsoft Theater in Los Angeles. “Rudy in Concert,” conducted by Justin Freer — the co-founder of CineConcerts, who studied with the late composer — will also feature a pre-show panel with Astin, director David Anspaugh, screenwriter Angelo Pizzo, producers Robert Fried and Cary Woods, Carol Goldsmith (the composer’s widow) and Ruettiger himself.

“I saw Jerry Goldsmith cry in the sound room with his wife, Carol, as they were scoring that movie,” says Ruettiger, who attended all of the scoring sessions at the now-extinct Todd-AO Scoring Stage. “He turned and said to me, ‘This music will be heard the rest of your life, Rudy. The rest of your life.’ I’ll never forget those words.”

Ruettiger was there every step of the movie-making journey, which he says began in the locker room after his famous tackle in the 1975 Notre Dame game against Georgia Tech. After a decade’s persistence — overcoming his small stature, dyslexia and poor grades — he fulfilled his childhood dream of making it into the Fighting Irish, and finally got to play in the final game of his final season. He tackled the opposing quarterback and got carried off the field.

“I don’t know if they were criticizing me or making fun of me in that locker room, when the guys said, ‘This only happens in Hollywood,’” says Ruettiger. “I’m going, ‘Dude, you don’t understand what I’ve been through in order to get to this point. This is real life, man. The reason why those people cheered is not because I made the tackle. I think they cheered because there was hope there. That’s what filtered through that stadium. The impossible became possible.’”

Ruettiger took his inspirational story to Hollywood twice without bearing any fruit. Unkept promises and an unused script came and went, and he took a job as an insurance salesman and then as a groundskeeper at a condo in South Bend, Indiana. His dreams were revitalized after he saw the 1986 underdog basketball movie, “Hoosiers” — directed by Anspaugh, written by Pizzo and scored by Goldsmith — and he eventually got his story to its team.

Finally, in 1993, TriStar Pictures made Rudy’s story into a movie. In other words, it took Rudy as long to get to Hollywood as it did to get onto the field at Notre Dame.

“The movie of ‘Rudy’ is not about football, it’s not about Rudy Ruettiger,” he insists. “It’s a message of hope. The same feeling I had when I saw my dad in church when they gave the Notre Dame score, how his eyes lit up with hope. He worked three jobs, we had 14 in the family — stressful life. But yet when Notre Dame won, it gave him hope. That’s a gift I wanted to give him. And that’s the gift I think we gave America.”

The film, which earned almost $23 million after it came out on October 22, 1993, routinely appears on lists of top sports movies. Among the hordes who have thanked Ruettiger over the years are former New England Patriots wide receiver Chris Hogan and former L.A. Lakers star Kobe Bryant, who both partly attributed their careers and work ethic to the film.

“You haven’t experienced what I’ve experienced,” says Astin, “with thousands and thousands of people, many of them big men — you know, hulking, football-sized men — who want to have an aside with me to tell me it was the first movie they cried during. I’ve been at the bedside of dying children — they’re in the bed in their living room, and they’ve got the movie up.”

And “it’s absolutely the music,” Astin says, that brings on the waterworks.

“I’ve always felt a sense of injustice within the Hollywood community about formally recognizing what Jerry accomplished with this score,” he says. “All composers know and love and revere Jerry, and they totally love this score. But he didn’t get an Academy Award nomination, which I just didn’t understand. I was just so upset when that happened.”

Goldsmith, who died in 2004, was a bit of an underdog himself. His prolific body of work for film and TV over 50 years rivaled that of his contemporary, John Williams, but he was rarely offered the beloved blockbusters and prestige pictures that Williams racked up. For every “Planet of the Apes” or “Chinatown,” there were five films like “Mom and Dad Save the World” and “Chain Reaction.” He only won a single Oscar, for 1976’s “The Omen.”

“Jerry was not the kind of guy to self-promote,” Anspaugh told me in 2017. “Combine that with the fact that sometimes it’s just the luck of the draw, you know, to have the right movie at the right time, and do big box office. But I mean, my God — his body of work…”

After he composed a bouncing, jubilant, synth-heavy score for “Hoosiers,” Goldsmith was eager to work with Anspaugh and Pizzo on another uplifting film. He was well-known for his work in the horror, sci-fi and action genres, but the composer had a soft spot for intimate, sincere dramas. “That’s one thing that Jerry and I share, in terms of our critics,” Anspaugh said. “He has been criticized for being too sentimental at times — as have I. And the other similarity is that neither one of us ever apologized for it. It’s just who we are.”

When he conducted concerts of his film music, Goldsmith nearly always included suites from these two sports films. When people asked him what his favorite scores were, he would often say “Hoosiers” and “Rudy.”

His fanfare for “Rudy,” a rousing brass tune that persists and strives along with the protagonist, has become shorthand for athletic glory and underdogs everywhere. It’s a staple of sporting events, from little leagues to the Olympics.

Then there’s the tender, almost lullaby-like melody for Rudy, which opens the film on solo flute. It’s a sensitive portrait of the real heart of the story — Rudy’s heart — and it passes from this childlike guise to a minor-key melancholy when hope starts to dim, before swelling into a magnificent hymn for full orchestra and choir.

“You have to be careful in movies like that — you really have to pick your spots,” said Anspaugh. “Because Rudy had all these obstacles thrown in front of him, and with every victory, you know, there would be an opportunity to go for the jugular. And then what do you have left at the end? I tried to steer away from those traps, as best I could, and Jerry did the same. But at the same time, we were true to what the material was, and what Angelo wrote.”

The Hollywood Chamber Orchestra will perform the score on Saturday — including some of the musicians who performed on the original recording, like pianist Mike Lang — along with the Cal State Fullerton University Singers.

When the score was first being recorded, Ruettiger asked Goldsmith if he could conduct the orchestra. “He says, ‘Sure!’” Ruettiger recalls, laughing. “And the orchestra, they were great — just great people. And they got excited, I got excited, and they let me do bar 64 and bar 65. Isn’t that awesome?”

He got to keep the baton.

During those sessions, Ruettiger befriended Goldsmith’s longtime music editor, Kenneth Hall. When Hall started teaching in the film scoring program at USC, he invited Ruettiger, now a motivational speaker, to come and inspire the prospective film composers. Hall passed away in 2016, but Ruettiger still comes every year. He’ll speak to the students on Thursday.

“If I didn’t go to practice every day and practice and practice, I would never have been prepared for that moment,” he says of his big play. “And that’s what I tell the film students: you practice and prepare like you’re scoring a movie — today. Because your time’s going to come, and you’re going to be ready. That’s what happened to me.”