Source : Webster's Revised Unabridged Dictionary (1913)

Obstructer \Ob*struct"er\, n.
   One who obstructs or hinders.

Source : WordNet®

obstructer
     n 1: someone who systematically obstructs some action that others
          want to take [syn: {obstructionist}, {obstructor}, {resister},
           {thwarter}]
     2: any structure that makes progress difficult [syn: {obstruction},
         {obstructor}, {impediment}, {impedimenta}]