Complex sentence: His 2005/2006 season proved disappointing, with a quarter-final appearance in the Welsh Open the highlight, as he failed to qualify for the World Championship, losing to Dave Harold, causing him to drop down the rankings.
Split into simpler sentences: His 2005/2006 season proved disappointing, with a quarter-final appearance in the Welsh Open the highlight. He failed to qualify for the World Championship losing to Dave Harold, causing him to drop down the rankings.