In act 1, scene 5, Romeo, Mercutio, Benvolio, and several of their friends attend the Capulet masquerade, which they were not invited to since they are Montagues and sworn enemies of the Capulet family. During the ball, Romeo sees Juliet for the first time and expresses his feelings of wonder and love for her aloud. While Romeo is singing Juliet's praises and comparing her to a "rich jewel in an Ethiope’s ear," Tybalt recognizes his voice and immediately calls for his sword with the intention of killing Romeo. Tybalt is portrayed as a hot-tempered man, who is obsessed with family loyalty and honor. Tybalt is deeply insulted and offended that Romeo would attend his family's masquerade uninvited and says,

"What, dares the slave Come hither, covered with an antic face, To fleer and scorn at our solemnity? Now, by the stock and honor of my kin, To strike him dead I hold it not a sin" (Shakespeare, 1.5.54-58).

When Tybalt explains to Lord Capulet that Romeo has come to mock his party and should immediately be punished, Lord Capulet instructs him to calm down and mentions Romeo's positive reputation throughout Verona. Tybalt proceeds to tell Lord Capulet that he will not endure Romeo's presence and Capulet challenges him by saying,

"You’ll make a mutiny among my guests. You will set cock-a-hoop. You’ll be the man!" (Shakespeare, 1.5.79-80).

Essentially, Lord Capulet does not feel that Romeo has any negative intentions and knows that he is not causing any problems. Lord Capulet also wants to be viewed as a gracious host and avoid trouble, which is why he forbids Tybalt from attacking Romeo.

Tybalt, a Capulet, recognizes Romeo's voice (even though his face is hidden by a mask) at his uncle's ball. He is outraged that Romeo would appear at his uncle's home, and is determined to kill him, telling his servant to get his rapier. Capulet, despite being the enemy of the Montague, forbids Tybalt to do so, first because he is under his roof, and second because he has heard that young Romeo is a "virtuous and well-govern'd youth". Tybalt protests, and Capulet insists that Romeo is not to be touched. This is a pivotal event in the play in more than one way. Capulet's forebearance allows his daughter to meet Juliet, and Tybalt's rage and hatred for Romeo will eventually lead to their disastrous duel in the streets. Given that the Chorus has already told the audience that Romeo and Juliet are to die, they can perhaps surmise that this event will have grave consequences.