Complex sentence: His fondness for drinking whisky at the board once led him to down an opponent's glass, saying, after the opponent had resigned shortly afterwards, "My opponent left a glass of whisky en prise and I took it en passant".
Split into simpler sentences: His fondness for drinking whisky at the board once led him to down an opponent's glass. Shortly afterwards, the opponent resigned, leading him to quip, "My opponent left a glass of whisky en prise and I took it en passant".