Complex sentence: Raced lightly, although Bold Reasoning set a new track record at Belmont Park for 6 furlongs at 4, he is best known as the sire of the 1977 Triple Crown winner, Seattle Slew.
Split into simpler sentences: Raced lightly, Bold Reasoning set a new track record at Belmont Park for 6 furlongs at 4. He is best known as being the sire of the 1977 Triple Crown winner, Seattle Slew.