Complex sentence: He spent many years managing at the Class AA level, working patiently with Boston prospects and in his only AAA managerial role, he was the last skipper in the history of the Minneapolis Millers of the American Association, in 1960.
Split into simpler sentences: He spent many years managing at the Class AA level, working patiently with Boston prospects. In his only AAA managerial role, he was the last skipper in the history of the Minneapolis Millers of the American Association, in 1960.