Complex sentence: After playing well in the reserves, he earned his first-team debut aged 20 after two games of the 1972/73 season, replacing the injured Tony Book, City beat Norwich City 3-0 at home on 19 August 1972.
Split into simpler sentences: After playing well in the reserves, he earned his first-team debut aged 20 after two games of the 1972/73 season. He played instead of the injured Tony Book as City beat Norwich City 3-0 at home on 19 August 1972.