After Romeo receives a death threat from Tybalt, Mercutio expects Romeo to engage Tybalt in a duel. However, Romeo refuses to fight Tybalt, as Tybalt is Juliet's cousin and therefore his kinsman. Not knowing this, Mercutio is incensed, and decides to fight Tybalt himself. Romeo, not wanting his best friend or his relative to get hurt, intervenes, causing Mercutio to be killed by Tybalt stabbing under Romeo's arm.
