Complex sentence: The Widener Handicap at Hialeah Park in Miami, Florida was a Grade I stakes race for 4-year-old and up Thoroughbred racehorses run over a distance of 1¼ miles (10 furlongs).
Split into simpler sentences: The Widener Handicap at Hialeah Park in Miami, Florida was a Grade I stakes race for Thoroughbred racehorses 4-years-old and up. It was run over a distance of 1¼ miles (10 furlongs).