Legal advice on injury waiver?

I am being asked to sign a waiver to play in a sports league. I am well aware of the inherit injury risks that are involved. However, at the bottom it says in large letters "EVEN IF ARISING FROM OUR NEGLIGENCE" and then at the bottom says "I FULLY UNDERSTAND THAT I HAVE GIVEN UP SUBSTANTIAL RIGHTS" Now I understand that I can not sign a waiver that blindly excuses negligence, is this a legal doent and will it hold up in court if I were injured due to their mistake?