Source : WordNet®

on the spot
     adv 1: without delay or immediately; "we hired her on the spot";
            "thought they were going to shoot us down on the spot"
     2: in a difficult situation; "that question really put him on
        the spot"
     3: at the place in question; there; "they were on the spot when
        it happened"; "it had to be decided by the man on the
        spot"