In Romeo and Juliet Act One - Scene Five Why does Tybalt become so upset, and how does Capulet respond to his rage?

He is upset because he sees Romeo at his party and their families do not like each other. Capulet tells him not to fight tonight, but Tybalt says that he wants to kill Romeo, but Capulet gets mad, and slaps Tybalt, because Capulet thinks that Romeo isn't trying to mess up the party, Romeo is just having fun, and talks gently without harming Juliet.