The Collaborative International Dictionary of English v.0.48:

Pick off \Pick" off\, v. t.
   1. (Baseball) to put out a baserunner who is off base by
      tagging him/her, especially by a quick throw from the
      pitcher or catcher.
      [PJC]

   2. to shoot so as to kill or disable, especially one by one
      from a position or in a situation where the target is
      unable to return fire at the shooter; -- used commonly of
      sniper fire. "The sniper picked off a dozen passersby from
      the tower before he was shot down by police."
      [PJC]

   3. (Football) to intercept (a pass).
      [PJC]

WordNet (r) 3.0 (2006):

pick off
    v 1: shoot one by one
    2: pull or pull out sharply; "pluck the flowers off the bush"
       [syn: pluck, tweak, pull off, pick off]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "pick off":
   charge, cock, detonate, discharge, drop, eject, fell, fire,
   fire off, gun, gun for, hit, let fly, let off, load, pelt, pepper,
   pistol, plug, pot, potshoot, potshot, prime, riddle, shoot,
   shoot at, shoot down, snipe, strike, take a potshot, torpedo