Benvolio foreshadows the trouble between the 2 families by warning Mercutio about the hot day.
He's dead!
Have I become a girl?
Tybalt shows up looking for Romeo. Mercutio is insulted by him and threatens to fight him. They use puns in order to insult each other.
Run!
Fire-eyed fury, be my conduct!
You're wretched!
Romeo shows up, Tybalt insults him. Romeo says he loves him- he only says that because he just married Juliet. Romeo then tries to stop Mercutio and Tybalt from fighting. Tybalt stabs Mercutio then runs.
Mercutio was killed by Tybalt. Tybalt was killed by Romeo, I swear!
You're all punished!
Romeo wonders if his love for Juliet has softened him and made him effeminate. Benvolio then runs to Romeo to tell him Mercutio's died.
Tybalt returns to finish the job and attempts to kill Romeo as well. Romeo kills him and then has to run away.
Prince, the Montagues, the Capulets, and others show up to find both Tybalt and Mercutio dead. The families argue about who to blame after Benvolio explains what happened. The Prince decides to banish Romeo and if he returns, he'll be killed.