Complex sentence: He was an important and regular part of the Charlton team, at the time managed by Alan Curbishley for the first two years, suddenly leaving the first team by 1998 and only making a handful of appearances from then on.
Split into simpler sentences: He was an important and regular part of the Charlton team, managed for the first two years by Alan Curbishley. Barness suddenly left the first team in 1998 and only made a handful of appearances from then on.