Complex sentence: Stengel agreed to terms with the Yankees, but the news was kept quiet so as not to be overshadowed by the 1948 World Series between the Cleveland Indians and Boston Braves, but there were rumors during the Series that Stengel was the Yankees' choice.
Split into simpler sentences: Stengel agreed to terms with the Yankees, but the news was kept quiet so as not to be overshadowed by the 1948 World Series between the Cleveland Indians and Boston Braves. Nevertheless, there were rumors during the Series that Stengel was the Yankees' choice.