How to show only certain items in an option set.....

Hello,

I have an option set field called Field B that has about 8 items in it.  When Field A = Football, I want only certain items to display, when Field A is something other than Football, I want all the options to display.  How can I do this?  I would prefer to do this in Java Script, just need some help writing it.

Hope this makes sense, thank you.