Complex sentence: The Braves had won the National League pennant for the first time since the "Miracle Braves" team of 1914 but the Indians spoiled a chance for the only all-Boston World Series by winning a one-game playoff against the Boston Red Sox.
Split into simpler sentences: The Braves had won the National League pennant for the first time since the "Miracle Braves" team of 1914. The Indians spoiled a chance for the only all-Boston World Series by winning a one-game playoff against the Boston Red Sox.