Complex sentence: He died from head injuries sustained in a spill on Feburary 4 when he was unseated after his mount, World Trade, broke down on the first turn of a $13,900 claiming race.
Split into simpler sentences: He died from injuries sustained in a spill on Feburary 4. He was unseated after his mount, World Trade, broke down on the first turn of a $13,900 claiming race.