The Collaborative International Dictionary of English v.0.48:

Coacher \Coach"er\, n.
   1. A coachman. [Obs.]
      [Webster 1913 Suppl.]

   2. A coach horse.
      [Webster 1913 Suppl.]

   3. One who coaches; specif. (Baseball), one of the side at
      the bat posted near first or third base to direct a base
      runner; also called a coach; as, third base coach.
      [Webster 1913 Suppl. +PJC]