in this scene Benvolio and mercutio was talking and benvolio had said that the capulet are patrolling and if we see them we wont escape a brawl but mercutio didnt care he was ready for a brawl. then tybalt had came and asked for romeo himself to fight and kill him,then romeo had came and told tybalt i love u more than u think i do but tybalt was not having it mercutio then stepped in and defend romeo and fought tybalt romeo tried to stop it but tybalt got h is sword under romeos arm and stabbed then tybalt and and minutes later mercutio died before his death mercutio said that there is a plage on both families, romeo had swore for revenge then tybalt returns and romeo engages him and in the end tybalt lost and was killed then romeo had fled. after the prince arrived and saw everything and  benvolio had told him everything and told on romeo so romeo had been sentenced to banishment.