Complex sentence: Five years after his departure Estíbariz returned to Athletic Bilbao, starting out as trainer for the youth sides--until 2009, he would work in that capacity with farm team CD Baskonia and the reserve squad.
Split into simpler sentences: Five years after his departure, Estíbariz returned to Athletic Bilbao starting out as trainer for the youth sides. Until 2009, he would work in that capacity with farm team CD Baskonia and the reserve squad.