Complex sentence: In April 1804, when Keats was eight, his father died from a skull fracture, suffered when he fell from his horse while returning from a visit to Keats and his brother George at school.
Split into simpler sentences: In April 1804, when Keats was eight, his father died. The cause of death was a skull fracture, suffered when he fell from his horse while returning from a visit to Keats and his brother George at school.