Complex sentence: They begin to duel with each other over who should get Emily, but are thwarted by the arrival of Theseus, who sentences them both to gather 100 men apiece and to fight a mass judicial tournament, the winner of which is to marry Emily.
Split into simpler sentences: They begin to duel with each other over who should get Emily, but are thwarted by the arrival of Theseus. Palamon and Arcite are to gather 100 men apiece and to fight a mass judicial tournament, the winner of which is to marry Emily.