What is the cause of violence in Romeo and Juliet Act 3, scene 1?
In Act 3, scene 1, Tybalt comes looking for Romeo to challenge him to fight because Tybalt is mightily offended that Romeo went to the Capulets' feast the night before. If you'll recall, Tybalt pointed Romeo out to Lord Capulet, but Lord Capulet told Tybalt that he was not allowed to attack Romeo at the party, because it would ruin the festivities and upset the other guests. Now, however, Tybalt wants to protect his family's honor by challenging Romeo.
At first, Romeo refuses to fight because he has just married Juliet in secret, and so Tybalt is now actually his relative by marriage. However, Mercutio thinks Romeo is behaving like a coward, and so he steps in to fight Tybalt instead. Romeo comes between them to try to keep the peace, and Tybalt stabs Mercutio under Romeo's arm. After Mercutio dies, having cursed both families, Romeo kills Tybalt and then flees.