skirmisher

from WordNet (r) 3.0 (2006)

skirmisher
    n 1: someone who skirmishes (e.g., as a member of a scouting
         party)

from The Collaborative International Dictionary of English v.0.48

Skirmisher \Skir"mish*er\, n.
   One who skirmishes. Specifically: pl. (Mil.) Soldiers
   deployed in loose order, to cover the front or flanks of an
   advancing army or a marching column.
   [1913 Webster]