Source : Webster's Revised Unabridged Dictionary (1913)

Touchback \Touch"back`\, n. (G)
   The act of touching the football down by a player behind his
   own goal line when it received its last impulse from an
   opponent; -- distinguished from safety touchdown.

Source : WordNet®

touchback
     n : (American football) a play in which the opposing team has
         kicked the football into your end zone