Complex sentence: Fenlon began playing "Dungeons & Dragons" when it was introduced in 1974, and by the late seventies he, S. Coleman Charlton and Kurt Fischer were developing a set of unique house rules for their six year campaign.
Split into simpler sentences: Fenlon began playing "Dungeons & Dragons" when it was introduced in 1974. By the late seventies he, S. Coleman Charlton and Kurt Fischer were developing unique house rules for their six year campaign.