What is "to run foul of"

Foul \Foul\ (foul), a. [Compar. Fouler (-[~e]r); superl. Foulest.] [OE. foul, ful, AS. f[=u]l; akin to D. vuil, G. faul rotten, OHG. f[=u]l, Icel. f[=u]l foul, fetid; Dan. fuul, Sw. ful foul, Goth. f[=u]ls fetid, Lith. puti to be putrid, L. putere to stink, be putrid, pus pus, Gr. py`on pus, to cause to rot, Skr. p[=u]y to stink. [root]82. Cf. Defile to foul, File to foul, Filth, Pus, Putrid.]

1. Covered with, or containing, extraneous matter which is injurious, noxious, offensive, or obstructive; filthy; dirty; not clean; polluted; nasty; defiled; as, a foul cloth; foul hands; a foul chimney; foul air; a ship's bottom is foul when overgrown with barnacles; a gun becomes foul from repeated firing; a well is foul with polluted water.

   My face is foul with weeping.
   --Job. xvi. 16.

2. Scurrilous; obscene or profane; abusive; as, foul words; foul language.

3. Hateful; detestable; shameful; odious; wretched. ``The foul with Sycorax.''
   --Shak.

   Who first seduced them to that foul revolt?
   --Milton.

4. Loathsome; disgusting; as, a foul disease.

5. Ugly; homely; poor. [Obs.]
   --Chaucer.

   Let us, like merchants, show our foulest wares.
   --Shak.

6. Not favorable; unpropitious; not fair or advantageous; as, a foul wind; a foul road; cloudy or rainy; stormy; not fair; -- said of the weather, sky, etc.

   So foul a sky clears not without a storm.
   --Shak.

7. Not conformed to the established rules and customs of a game, conflict, test, etc.; unfair; dishonest; dishonorable; cheating; as, foul play.

8. Having freedom of motion interfered with by collision or entanglement; entangled; -- opposed to clear; as, a rope or cable may get foul while paying it out.

   Foul anchor. (Naut.) See under Anchor.

   Foul ball (Baseball), a ball that first strikes the ground outside of the foul ball lines, or rolls outside of certain limits.

   Foul ball lines (Baseball), lines from the home base, through the first and third bases, to the boundary of the field.

   Foul berth (Naut.), a berth in which a ship is in danger of fouling another vesel.

   Foul bill, or Foul bill of health, a certificate, duly authenticated, that a ship has come from a place where a contagious disorder prevails, or that some of the crew are infected.

   Foul copy, a rough draught, with erasures and corrections; -- opposed to fair or clean copy. ``Some writers boast of negligence, and others would be ashamed to show their foul copies.''
   --Cowper.

   Foul proof, an uncorrected proof; a proof containing an excessive quantity of errors.

   Foul strike (Baseball), a strike by the batsman when any part of his person is outside of the lines of his position.

   To fall foul, to fall out; to quarrel. [Obs.] ``If they be any ways offended, they fall foul.''
   --Burton.

   To fall foul of or To run foul of. See under Fall.

   To make foul water, to sail in such shallow water that the ship's keel stirs the mud at the bottom.