In my last USCF game in Wisconsin, I played Rc8 in the following position:
I called that move a sacrifice, but many did not agree. WI expert John Becker had this to say:
[It is a pleasing combination that forces the win of material based on taking advantage of overloaded and/or unprotected pieces, but in no way, shape or form can it be considered a "sac".]
To settle the issue I sent in the question to GM Larry Evans, and he replied in the current version of Chess Life for kids: Link here
If you can't get to the link here is the question and answer:
Q: Can you please settle this debate? In this position I played 26.Rc8. Does this move fit the definition of a sacrifice?
A: A sacrifice—whether sound or unsound—is generally understood as a move that gives up material intending to get something good in return. A gambit, for example, usually is a sacrifice in the opening that offers a pawn for speedy development. Here 26.Rc8! (ignoring the knight hanging on f3) could be defined as a temporary and sound sacrifice since after 26...Rxc8 27.Nxe7+ Kg7 28.Nxc8 Qc7 29.Qc2 Qxc2 30.Bxc2 gxf3 31.gxf3 White simplifies to a winning ending a pawn ahead.