Romeo kills Tybalt because Tybalt kills Mercutio, who is Romeo's close friend. Initially, Tybalt insults Romeo and challenges him to a fight, but Romeo refuses to fight because he has just secretly married Juliet, Tybalt's cousin, and now considers Tybalt family. Mercutio, angered by Romeo's refusal, fights Tybalt instead. During the fight, Tybalt fatally stabs Mercutio under Romeo's arm. Enraged by the death of Mercutio, Romeo seeks revenge and kills Tybalt in a duel. This act leads to Romeo's banishment from Verona by the Prince, escalating the tragic events of the play.
In summary, Romeo kills Tybalt out of grief and revenge for Mercutio's death, despite Romeo's initial intention to avoid fighting Tybalt due to his new family ties. This moment marks a key turning point in Shakespeare's "Romeo and Juliet" as it triggers Romeo's exile and deepens the feud between the Capulets and Montagues.
