The black is not dirt. It is plate. In slowpitch if the pitch hits the black it has hit the plate and should be called a ball. PERSONNALLY... as an umpire cover the black (at the back of the plate) with dirt and call strikes when the dirt is hit by the pitch. PERSONNALLY... leave the black at the sides of the plate visible - it makes for a wider plate and more strike calls. A pitch that hits the black on the side of the plate is well short and should be called a ball.
Original question about FORCE PLAY - in FED rule book see rule 2-24: a force play is a play in which the runner loses the right to the base occupied and is forced to advance because the batter becomes a batter-runner.
This means the base occupied is not a sanctuary and the runner standing on the base is in immediate jeopardy (to be tagged out) - she/he must advance. If tagged while standing on a base from which they are forced to leave, they are out. This is true unless the force has been removed by tagging the base prior to tagging the runner. (You are correct BigJohnUmp.)
This is more than JMHO.
