Complex sentence: According to his mother, Ashburn planned on retiring from broadcasting at the end of the 1997 season, but he died unexpectedly of a heart attack in New York City at age 70, after broadcasting a Phillies-Mets game at Shea Stadium.
Split into simpler sentences: According to his mother, Ashburn planned on retiring from broadcasting at the end of the 1997 season. He died of a heart attack in New York City at age 70, after broadcasting a Phillies-Mets game at Shea Stadium.