A Melee attack is a standard move among all Pros. By default, the attack is performed by clicking the right stick in or on the PC version by hitting the C key. All Melee attacks do a standard, small amount of damage, and, like the Assassin's Dagger and Sword, do more damage when you attack from behind. Juiced Melee attacks do significantly increased damage. It is possible to earn the "Humiliation" ProTag by killing an enemy player with a melee attack (For the Assassin, it must be the Melee attack, which is a kicking action, not the Dagger/Sword weapon attack). One consistent possibility may arise when an Assassin attempts an assassination but the enemy barely survives. Following through with a Melee stands a chance of both the Kill and the ProTag.
Melee attacks give a good amount of Juice to the attacker—roughly 5% of the Juice bar—regardless of whether they strike Bullseye, the Money Ball, or an enemy Pro or Bot. Melee attacks do not garner any juice from, nor do they do any damage to Turrets.