How do you say diamond backs in Spanish?
If you are referring to the Sports-team, it is a name and most
people would just say "Diamondbacks" although the last "d" would be
sort of silent, because of Spanish pronunciation conventions.
If you literally wish to say "diamond backs" as in "backs" made
up of "diamonds" (in the same way that "silk scarves" are "scarves"
made up of "silk"), you can say "espaldas de diamantes".