Complex sentence: Sprang's name never appeared on his Batman work during his career, due to stipulations in Bob Kane's contract which stated that Kane would have sole credit as Batman's creator, regardless of whether he worked on any particular story.
Split into simpler sentences: Sprang's name never appeared on his work during his career, due to stipulations in Bob Kane's contract. This contract stated that Kane would have sole credit as Batman's creator, regardless of whether he worked on any particular story.