Complex sentence: He successfully appealed in the U.S. Supreme Court, which overturned his conviction in 1971, by which time he had not fought for nearly four years--losing a period of peak performance as an athlete.
Split into simpler sentences: He successfully appealed in the U.S. Supreme Court, which overturned his conviction in 1971. By that time, he had not fought for nearly four years--losing a period of peak performance as an athlete.