In late 1975, the heavyweight boxing world champion, Apollo Creed, announces plans to hold a title bout in Philadelphia during the upcoming United States Bicentennial. However, he is informed five weeks from the fight date that his scheduled opponent is unable to compete due to an injured hand. With all other potential replacements booked up or otherwise unavailable, Creed decides to spice things up by giving a local contender a chance to challenge him. He settles in on Rocky Balboa, an aspiring southpaw boxer from an Italian neighborhood of Philadelphia, known by the nickname "The Italian Stallion".

Rocky meets with promoter Miles Jergens, unexpectedly presuming Creed is seeking local sparring partners. Reluctant at first, Rocky eventually agrees to the fight which will pay him $150,000. After several weeks of training, using whatever he can find, including meat carcasses as punching bags, Rocky accepts an offer of assistance from former boxer Mickey "Mighty Mick" Goldmill, a respected trainer and former bantamweight fighter from the 1920s, who always criticized Rocky for wasting his potential.

Meanwhile, Rocky meets Adrian Pennino, who is working part-time at the J&M Tropical Fish pet store. He begins to build a romantic relationship with Adrian, culminating in a kiss. Adrian's brother, Paulie, becomes jealous of Rocky's success, but Rocky calms him by agreeing to advertise his meatpacking business before the upcoming fight. The night before the fight, Rocky begins to lose confidence after touring the arena. He confesses to Adrian that he does not expect to win, but is content to go the distance against Creed and prove himself to everyone.

On New Year's Day, the fight is held, with Creed making a dramatic entrance dressed as George Washington and then Uncle Sam. Taking advantage of his overconfidence, Rocky knocks him down in the first round—the first time that Creed has ever been knocked down. Humiliated, Creed takes Rocky more seriously for the rest of the fight, though his ego never fully fades. The fight goes on for the full fifteen rounds, with both combatants sustaining various injuries. As the fight progresses, Creed's superior skill is countered by Rocky's apparently unlimited ability to absorb punches, and his dogged refusal to go down. As the final round bell sounds, with both fighters locked in each other's arms, they promise to each other that there will be no rematch.

After the fight, the sportscasters and the audience go wild. Jergens announces over the loudspeaker that the fight was "the greatest exhibition of guts and stamina in the history of the ring", and Rocky calls out repeatedly for Adrian, who runs down and comes into the ring as Paulie distracts arena security. As Jergens declares Creed the winner by virtue of a split decision (8:7, 7:8, 9:6), Adrian and Rocky embrace and profess their love to each other, not caring about the result of the fight.

Development

Sylvester Stallone wrote the screenplay for Rocky in three and a half days, shortly after watching the championship match between Muhammad Ali and Chuck Wepner that took place at Richfield Coliseum in Richfield, Ohio on March 24, 1975. Wepner was TKO'd in the 15th round of the match by Ali, but nobody ever expected him to last as long as he did. Despite the fact that the match motivated Stallone to begin work on Rocky, he has subsequently denied that Wepner provided any inspiration for the script. Other possible inspirations for the film may have included characteristics of real-life boxers Rocky Marciano and Joe Frazier, as well as Rocky Graziano's autobiography Somebody Up There Likes Me and the movie of the same name. Wepner filed a lawsuit which was eventually settled with Stallone for an undisclosed amount.

United Artists liked Stallone's script, and viewed it as a possible vehicle for a well-established star such as Robert Redford, Ryan O'Neal, Burt Reynolds, or James Caan. Stallone insisted upon portraying the title character himself, to the point of issuing an ultimatum. Stallone later said that he would never have forgiven himself, had the film become a success with somebody else in the lead. He also knew that producers Irwin Winkler and Robert Chartoff's contract with the studio enabled them to "greenlight" a project if the budget was kept low enough. The producers also collateralized any possible losses with their big-budget entry, New York, New York (whose eventual losses were covered by Rocky's success). The film's production budget ended up being $1,075,000, with a further $100,000 spent on producers' fees and $4.2 million on advertising costs.

Casting

Although Chartoff and Winkler were enthusiastic about the script and the idea of Stallone playing the lead character, they were hesitant about having an unknown headline the film. The producers also had trouble casting other major characters in the story, with Apollo Creed and Adrian cast unusually late by production standards (both were ultimately cast on the same day). Real-life boxer Ken Norton was initially sought for the role of Apollo Creed, but he pulled out and the role was ultimately given to Carl Weathers. Norton had had three fights with Muhammad Ali, upon whom Creed was loosely based. According to The Rocky Scrapbook, Carrie Snodgress was originally chosen to play Adrian, but a money dispute forced the producers to look elsewhere. Susan Sarandon auditioned for the role but was deemed too pretty for the character. After Talia Shire's ensuing audition, Chartoff and Winkler, along with Avildsen, insisted that she play the part.

Boxer Joe Frazier has a cameo appearance in the film. The character of Apollo Creed was influenced by outspoken boxer Muhammad Ali who fought Frazier three times. During the 49th Academy Awards ceremony in 1977, Ali and Stallone staged a brief comic confrontation to show Ali was not offended by the film. Some of the plot's most memorable moments—Rocky's carcass-punching scenes and Rocky running up the steps of the Philadelphia Museum of Art, as part of his training regimen—are taken from the real-life exploits of Joe Frazier, for which he received no credit.

Due to the film's comparatively low budget, members of Stallone's family played minor roles. His father rings the bell to signal the start and end of a round, his brother Frank plays a street corner singer, and his first wife, Sasha, was stills photographer. Other cameos include former Philadelphia and then-current Los Angeles television sportscaster Stu Nahan playing himself, alongside radio and TV broadcaster Bill Baldwin; and Lloyd Kaufman, founder of the independent film company Troma, appearing as a drunk. Diana Lewis, then a news anchor in Los Angeles and later in Detroit, has a small scene as a TV news reporter. Tony Burton appeared as Apollo Creed's trainer, Tony "Duke" Evers, a role he would reprise in the entire Rocky series, though he is not given an official name until Rocky II. Though uncredited, Michael Dorn, who would later gain fame as the Klingon Worf in Star Trek: The Next Generation and Star Trek: Deep Space Nine, made his acting debut as Creed's bodyguard.

Filming

Principal photography for Rocky began on January 9, 1976. Filming took place primarily throughout Philadelphia, with a few scenes being shot in Los Angeles. Inventor/operator Garrett Brown's new Steadicam was used to accomplish smooth photography while running alongside Rocky during the film's Philadelphia street jogging/training sequences and the run up the Art Museum's flight of stairs, now colloquially known as the Rocky Steps. It was also used for some of the shots in the fight scenes and can be seen at the ringside during some wide shots of the final fight. Rocky is often erroneously cited as the first film to use the Steadicam, although it was actually the third, after Bound for Glory and Marathon Man.

Certain elements of the story were altered during filming. The original script had a darker tone: Mickey was portrayed as racist, and the script ended with Rocky throwing the fight after realizing he did not want to be part of the professional boxing world after all.

During filming, both Stallone and Weathers suffered injuries during the shooting of the final fight; Stallone suffered bruised ribs and Weathers suffered a damaged nose, the opposite injuries of what their characters had.

The first date between Rocky and Adrian, in which Rocky bribes a janitor to allow them to skate after closing hours in a deserted ice skating rink, was shot that way only because of budgetary pressures. This scene was originally scheduled to be shot in a skating rink during regular business hours. However, the producers decided that they could not afford to hire the hundreds of extras that would have been necessary for that scene.

The poster seen above the ring before Rocky fights Apollo Creed shows Rocky wearing red shorts with a white stripe when he actually wears white shorts with a red stripe. When Rocky points this out, he is told that "it doesn't really matter, does it?" According to director Avildsen's DVD commentary, this was an actual mistake made by the props department that they could not afford to rectify, so Stallone wrote the brief scene to ensure the audience did not see it as a goof. (Carl Weathers, coincidentally, wore white-striped red shorts for the Creed-Balboa rematch in Rocky II.) Avildsen said that the same situation arose with Rocky's robe. When it came back from the costume department, it was far too baggy for Stallone. Because the robe arrived on the day of filming the scene and there was no chance of replacing or altering it, instead of ignoring this and risking the audience laughing at it, Stallone wrote the dialogue where Rocky himself points out the robe is too big.

Music

The musical score for Rocky was composed by Bill Conti, who previously composed a score for director John G. Avildsen's W.W. and the Dixie Dancekings (1975) that was ultimately rejected by the studio. In fact, David Shire (then-husband of Talia Shire) was the first to be offered the chance to compose the music for Rocky but had to turn it down due to prior commitments. Thus, Avildsen reached out to Conti without any studio intervention due to