Complex sentence: Higgins also clashed with with his managerial successor, Johnny Pesky, who had been personally chosen by Yawkey; by the end of the 1964 season, Higgins had pushed Pesky aside, replacing him with his own man, Billy Herman.
Split into simpler sentences: Higgins also clashed with with his managerial successor, Johnny Pesky, who had been personally chosen by Yawkey. By the end of the 1964 season, Higgins had pushed Pesky aside, replacing him with his own man, Billy Herman.