Complex sentence: Rosas then joined another club in the second division, CD Castellón, in 2005--06; after a slow first year, he became an undisputed starter, adding 16 league goals in the following three combined.
Split into simpler sentences: Rosas then joined another club in the second level, CD Castellón, in 2005--06. After a slow first year he became an undisputed starter, adding 16 league goals in the following three combined.