Leonard Bernstein's overture plays. We then see New York City, shot from above; the streets, the bridges, the skyscrapers. The camera zooms in on a group of Jets, the white gang, snapping their fingers on a basketball court. They walk past a girl drawing herself into the middle of a circle with chalk. They steal a basketball from two boys and play with it before tossing it back to one of the boys.
As they walk down the street, they begin to dance. Suddenly they run into Bernardo, the leader of the Sharks (the Puerto Rican gang), who stares at them silently. Riff, the leader of the Jets, laughs at Bernardo, and the Jets continue on. After two Jets follow Bernardo and whistle at him, Bernardo pounds the wall with his fist and begins walking alongside two Sharks, who break into their own dance with him. They run into the Jets, who heckle them as they walk past.
We see the Jets playing basketball, and Riff accidentally throws the basketball into Bernardo's hands. Bernardo stares at Riff before passing the ball back reluctantly. When one of the Sharks spits on one of the Jets, a fight breaks out between the two gangs. We see Sharks throw yellow paint on a group of Jets, then a group of Jets chasing Sharks over a large pile of rubble.
When Bernardo finds a Jet painting "Sharks Stink" on a wall, he and a number of Sharks surround the Jet and the Jet makes a run for it. A large fight breaks out between Sharks and Jets. The scuffle is interrupted by the whistle of Lieutenant Schrank and Officer Krupke, local police officers. Schrank calls a Jet named Baby John over and asks him to identify the Puerto Rican who beat him up. Riff interrupts him to jokingly suggest that they suspect it was a cop who beat Baby John up.
"You hoodlums don't own these streets, and I've had all the roughhouse I'm gonna put up with around here!" Schrank yells at the gangs. When Schrank is done, Bernardo sarcastically asks him to translate it into Spanish and everyone laughs. As the Sharks leave, Schrank complains about the state of the neighborhood and the fact that if he doesn't get some "law and order" in the neighborhood, he'll be demoted to traffic cop.
After Schrank leaves, Riff leads the gang down an alley. A girl called Anybodys follows them and begs to be let into the gang, but they deny her. Riff lectures the Jets about the fact that they cannot let the Puerto Ricans take over the neighborhood and must stage a rumble to teach the Sharks a lesson. The Jets discuss the fact that the Sharks could use blades or guns in the fight and that they should be careful. Riff tells them they have to match the Sharks even if it involves blades or guns, and that he will bring another Jet, Tony, to a war council to arrange the rumble with Bernardo. A Jet named Action is skeptical about bringing Tony into it, as Tony hasn't been around; "How come he takes a lousy stinkin' job?" Action says.
Riff insists that Tony will help them, singing a song about the loyalty of Jets for one another ("When You're a Jet"). The Jets discuss the fact that there's a dance at the gym that night and the Sharks will be there. That's where Riff plans to challenge Bernardo.
Riff visits Tony, his best friend, and is disappointed to hear that Tony isn't interested in initiating a rumble. Tony tries to convince Riff that getting a job is worthwhile, and that they ought not to pick fights with Sharks. "Four and a half years I live with guy and his family," Riff says, "I think I'm diggin' a guy's character. Boy, am I a victim of disappointment in you."
Tony tells Riff that recently he's been waking up reaching out for something, waiting for something exciting to happen to him. Riff asks him to come to the dance, and Tony eventually agrees. As Riff leaves, Tony sings a song about his feeling of expectancy and anticipation ("Something's Coming").
The opening shots of West Side Story set the scene for the film, dropping the viewer down in New York City. We see New York shot from high above; the streets, buildings, and bridges make tidy geometric shapes, and the cars are as small as insects, moving along in tidy rows. All we can hear in these opening moments is the rattle of a drum and a distant whistle. These shots and the sonic environment gives the impression of spaciousness, as if the city is a big empty playground, even though we can see from the scale of the buildings and the number of cars on the road that it is a bustling metropolis.
In a striking move by director Robert Wise, the entire first ten minutes of the film are in complete silence. No words are spoken by any of the characters, an unusual feature in any movie, but especially a musical. We watch as the antagonistic gangs, the Sharks and the Jets, circle each other and run through their neighborhood getting into trouble, but no one utters a word. This only adds to the sense that the two gangs are somehow alone, that the city is larger and more cavernous than it appears, empty apart from the rivalry between the two gangs.
Also notable about the opening moments of the film is the contrast between the tough characters, the Jets and the Sharks, and the way that they move, slowly breaking into balletic Jerome Robbins choreography in the middle of the street. While the characters dress like hoodlums, they have the poise and elegance of ballet dancers, breaking into elevated and athletic choreography. Additionally, the brilliance of this contrast comes from the fact that it is an extension of their movement, rather than a jarring juxtaposition. Their self-assured movement is an extension of their pack mentality, their power in the neighborhood, and their youthful confidence.
At the center of the film is an anxiety about immigration and scarcity. The Jets are worried that the Sharks are "taking over" the neighborhood, and that they will take everything away from them. They believe that, as white New Yorkers, they are entitled to more of the city's benefits than the Sharks. Riff wants to defend their neighborhood no matter what, and he insists that they have to fight to make sure that the Sharks do not get too cocky.
Tony is the protagonist of the film and Riff's best friend, and after finding a job at Doc's store, has an entirely different attitude towards the gang life. Working in the store has broadened Tony's perspective, and he thinks that Riff's time would be better spent trying to grow up rather than picking fights with a rival gang. Tony is at once practical and starry-eyed, a bit of a dreamer, who is sure that he has good things coming his way. He is one of the only Jets who seems to be thinking beyond the neighborhood rivalries and dreaming about a better life.