The Collaborative International Dictionary of English v.0.48:

Afoul \A*foul"\, adv. & a. [Pref. a- + foul.]
   In collision; entangled. --Totten.
   [1913 Webster]

   To run afoul of, to run against or come into collision
      with, especially so as to become entangled or to cause
      injury.
      [1913 Webster]