Complex sentence: Tommy then moved to Swindon Town for the 2003/2004 season, then in the summer of 2004 became a traitor when he left for Oxford United, Swindons bitter rivals finishing top scorer for the club in the 2004/2005 season.
Split into simpler sentences: Tommy then moved to Swindon Town for the 2003/2004 season. Then in the summer of 2004 became a traitor when he left for Oxford United, Swindons bitter rivals finishing top scorer for the club in the 2004/2005 season.