Source : Webster's Revised Unabridged Dictionary (1913)

Defensively \De*fen"sive*ly\, adv.
   On the defensive.

Source : WordNet®

defensively
     adv 1: in an apologetic and self-defensive manner; "`I felt it
            better you should know,' said Sir Cedric defensively"
     2: in a defensive manner; "the general conviction that our side
        is in the right and acting defensively over what Russians
        call the German question and Americans the Berlin crisis"
        [ant: {offensively}]