An attacking king in front of its own rook pawn can be sealed in: the defender simply shuttles between c7 and c8 and the position ends in stalemate.
White's king has run ahead of its pawn to a7, and the black king is on d7. With a centre pawn, a king in front of the pawn on the seventh would be overwhelming; with a rook pawn it is harmless, provided Black keeps the white king boxed in.