In Romeo and Juliet Act 3 Scene 1 who does Mercucio accuse of being a coward why?

In Act 3 Scene 1 of Romeo and Juliet, Romeo and Mercutio discuss Tybalt's challenge to a duel. Mercutio begins by accusing Tybalt of being a "villain" and a "coward" because he insists on fighting Romeo by the rules of courtly love, rather than engaging in a more spontaneous and violent brawl. Mercutio argues that Tybalt is hiding behind the rules of honor in order to avoid a truly dangerous confrontation, and he accuses Romeo of being too passive and willing to accept Tybalt's challenge without question.