Complex sentence: In the 1961--62 season, it achieved its best ever classification in the category after finishing fifth; however, as the main squad was relegated in La Liga, it was ineligible for promotion, being relegated instead.
Split into simpler sentences: In the 1961--62 season, it achieved its best ever classification in the category after finishing fifth. However, as the main squad was relegated in La Liga, it was ineligible for promotion, being relegated instead.