Expert: Steve L - 4/27/2004

Question
If a fielder drops or misplays a ball in foul territory WITHOUT any outside interference (fans or trees), is it considered an error? Does the amount of outs or guys on base at the time make a difference as to whether the play is an error or not?

Answer
The short answer to your question is Yes, it's considered an error.

According to the official rules, the key is whether the dropped foul ball PROLONGS THE TIME AT BAT OF THE BATTER, THE LIFE OF A RUNNER OR PERMITS A RUNNER TO ADVANCE.
See NOTE 3 (a) below


RULES
10.13 An error shall be charged for each misplay (fumble, muff or wild throw) which prolongs the time at bat of a batter or which prolongs the life of a runner, or which permits a runner to advance one or more bases.

NOTE (2) It is not necessary that the fielder touch the ball to be charged with an error. If a ground ball goes through a fielder's legs or a pop fly falls untouched and in the scorer's judgment the fielder could have handled the ball with ordinary effort, an error shall be charged.

NOTE (3) Mental mistakes or misjudgments are not to be scored as errors unless specifically covered in the rules.

(a) An error shall be charged against any fielder when he muffs a foul fly, to prolong the time at bat of a batter whether the batter subsequently reaches first base or is put out.