In the Prologue, a conflict between two rival teenage gangs, the Jets (2nd generation Americans) and the Sharks (Puerto Ricans) is enacted through dance. Most of the scene is silent. The tension between the gangs is quite visible. The boys are struggling for control of the neighborhood. Accented by police whistles and taunting phrases, the Prologue establishes the fierce rivalry between the two groups.
Following a brief exchange with the ineffective policemen, Lt. Schrank and Officer Krupke, Riff, the leader of the Jets, devises a plan to gain control of the street ("The Jet Song"). The members of the gang boast of their strength, restate their bond to one another and declare their intention to protect their turf. Riff and the Jets decide to initiate a rumble, with control of the neighborhood as a prize for the winning gang.