The hard vs. soft c in Celtic has been fought out for a long time, and not only in the context of the sports franchise. In Greek and Latin, our source for the word, the c in Celtic is hard (of course, in Greek it's not a c but a k or kappa). In English, c followed by e softens. So, technically speaking, the Boston team has it right in terms of modern English; the Celtic=Keltic contingent has it right in terms of the source languages. Let's hear it for K/Celtic s/civilization and S/Celtic k/culture!