I would like to ask if It is legal to under promote a pawn to opponents pieces? I mean like promoting white's pawn to a black's knight here will be a win. Here's the position for white;
Rc7 and for black;
[FEN "r7/kPR5/8/K7/8/8/8/8 w - - 0 1"] [Title "Underpromotion"]
Hope to hear from you, many thanks.