The Collaborative International Dictionary of English v.0.48:

Scratch \Scratch\, n.
   1. A break in the surface of a thing made by scratching, or
      by rubbing with anything pointed or rough; a slight wound,
      mark, furrow, or incision.
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            The coarse file . . . makes deep scratches in the
            work.                                 --Moxon.
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            These nails with scratches deform my breast.
                                                  --Prior.
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            God forbid a shallow scratch should drive
            The prince of Wales from such a field as this.
                                                  --Shak.
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   2. (Pugilistic Matches) A line across the prize ring; up to
      which boxers are brought when they join fight; hence,
      test, trial, or proof of courage; as, to bring to the
      scratch; to come up to the scratch. [Cant] --Grose.
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   3. pl. (Far.) Minute, but tender and troublesome,
      excoriations, covered with scabs, upon the heels of horses
      which have been used where it is very wet or muddy. --Law
      (Farmer's Veter. Adviser).
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   4. A kind of wig covering only a portion of the head.
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   5. (Billiards)
      (a) A shot which scores by chance and not as intended by
          the player; a fluke. [Cant, U. S.]
      (b) a shot which results in a penalty, such as dropping
          the cue ball in a pocket without hitting another ball.
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   6. In various sports, the line from which the start is made,
      except in the case of contestants receiving a distance
      handicap.
      [Webster 1913 Suppl.]

   Scratch cradle. See Cratch cradle, under Cratch.

   Scratch grass (Bot.), a climbing knotweed (Polygonum
      sagittatum) with a square stem beset with fine recurved
      prickles along the angles.

   Scratch wig. Same as Scratch, 4, above. --Thackeray.

   start from scratch to start (again) from the very
      beginning; also, to start without resources.
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