Complex sentence: He made his first team debut on the last day of the 2002--03 season with the team having already been relegated and he suffered a second relegation the following season, during which he made 19 appearances.
Split into simpler sentences: He made his first-team debut on the last day of the 2002--03 season with the team having already been relegated. Young suffered a second relegation the following season, in which he made 19 appearances.