Based on Romeo's reason for being at the party and Tybalt's response to seeing Romeo, how is Tybalt a foil for Romeo?

Tyrant foiled Romeo's night with Juliet after spotting the lovers dancing together, as he promptly reported the presence of a Montague at the Capulet hosted ball/party to his elders, Juliet's parents. Upon hearing of this intrusion, Romeo was immediately chased out.