It was like 10 books, I think, that started off set in the future following a cybernetically enhanced football player in games where players die ends up with the same character in a swords and sorcery fantasy environment. Something about him being immortal except being stabbed in the heart because a leaf fell on his chest over his heart when he became immortal I think and a magic cape? (it's been a long time since I read it in the school library)
I was 14 when I read it and it's been over 20 years think it was only the 1st book that had the football with a solid steel ball there was a war or revolt he ended up king or commander, got married that's all I can remember. the most memorable was that the series started really sci-fi cybernetic enhancements and spaceships then changes to pure fantasy, magic no technology.
The only other thing I can remember is valiant was maybe part name of one of the books and or the main characters name