Complex sentence: Yoshinaka was struck dead by an arrow when his horse became mired in a paddy field, and after Kanehira heard that Yoshinaka had been killed, he committed suicide by leaping off his horse while holding his sword in his mouth.
Split into simpler sentences: Yoshinaka was struck dead by an arrow when his horse became mired in a paddy field. Kanehira committed suicide by leaping off his horse while holding his sword in his mouth.