Question: What team won a two-leg Spanish football match played on 20 August and 23 August 1997, which one contestant won the 66th since its establishment, started on 31 August 1996 and finished on 23 June 1997?
Sentence (from "1996–97 La Liga"): The 1996–97 La Liga season, the 66th since its establishment, started on 31 August 1996 and finished on 23 June 1997.
Relevant evidence: Yes