Complex sentence: Arjuna's young son Abhimanyu is able to penetrate the formation, however, he is trapped when Jayadratha, the king of Sindhu holds the Pandava warriors following him at bay.
Split into simpler sentences: Arjuna's young son Abhimanyu was able to penetrate the formation. However, he was trapped when Jayadratha, the king of Sindhu, held the Pandava warriors following him at bay.