Complex sentence: After the retirement of Pelé in 1977, much of the progress that American soccer had made during his stay was lost; there was no star at the same level to replace him as the NASL's headline act.
Split into simpler sentences: After the retirement of Pelé, much of the progress that American soccer had made during his stay was lost. There was no star at the same level to replace him as the NASL's headline act.