Act 3 scene 1 summary of key points:
Benvolio and Mercutio are in the street, but Benvolio is anxious not to meet the Capulets as he feels sure there will be another brawl.
Tybalt enters, looking for Romeo; Mercutio is easily provoked by Tybalt.
Romeo enters. Tybalt insults him, but Romeo tries to keep things peaceful. This enrages Mercutio even more, and he starts to fight Tybalt.
Romeo tries to come between them to stop the fight, but Mercutio is fatally wounded.
Romeo is in turmoul as a result of Mercutio's death. He turns on Tybalt and kills him. Romeo flees.
The Prince learns of the details of the fight from Benvolio. Romeo is banished from Verona.
Why is this scene important?
The scene shows where the violence in the opening scene can lead.
We see Romeo torn between his new marriage into the Capulet family and his desire to protect and avenge his own kinsman following Tybalt's attack.
The scene provides evidence of how circumstances can turn a peace-loving man into a killer, as Romeo kills Tybalt.
It is at this point in the play that the events turn against Romeo and threaten his future with Juliet.