Complex sentence: The old, long rectangular stadium was heavily renovated and divided into two venues, becoming the square Louis Armstrong Stadium, with the remaining third becoming the attached Grandstand, the third largest stadium at the US Open, with a seating capacity of about 6,000.
Split into simpler sentences: The old, long rectangular stadium was heavily renovated and divided into two venues, becoming the square Louis Armstrong Stadium, with the remaining third becoming the attached Grandstand. Attached to the Louis Armstrong Stadium is the Grandstand, the third largest stadium at the US Open, with a seating capacity of about 6,000.