Complex sentence: He was considered a prospect for the 1980 Olympic Games (held in Moscow), but the U.S. boycotted the event, and Green also lost to Marvis Frazier in the quarterfinals of the Olympic Trials that year.
Split into simpler sentences: He was considered a prospect for the 1980 Olympic Games (held in Moscow), but the U.S. boycotted the event. However, Green also lost to Marvis Frazier in the quarterfinals of the Olympic Trials that year.