double base

[Shmuelg]

FWIW, as far as ISF is concerned, Rule 2, Sec.4h-1 states (bold by me):

"NOTE: THE FOLLOWING RULES APPLY TO THE DOUBLE BASE:
a) A batted ball hitting the fair portion is declared fair, and a batted ball hitting the foul portion only is declared foul.
b) If a play is made at first base on any batted ball, or (FP ONLY) the batter runs on a dropped third strike, and the batter-runner touches only the fair portion, and if the defense appeals prior to the batter-runner returning to first base, the batter-runner is out.

NOTE: This is treated the same as missing the base.

c) A defensive player must use only the fair portion of the base at all times.

EXCEPTION: On any live ball play made from first base foul territory, the batter-runner and the defensive player may use either base.

d) After over-running the base, the batter-runner must return to the fair portion.
e) On balls hit to the outfield when there is no play being made at the double base, the batter-runner may touch either portion of the base.
f) When tagging up on a fly ball, the fair portion must be used.
g) On an attempted pick-off play, the runner must return to the fair portion.
h) Once a runner returns to the fair portion, should he stand on the foul portion only, it is considered not in contact with the base and the runner shall be called out, if
1) He is tagged with the ball, or
2) He leads off from the foul portion on a pitched ball.

So, I understand that according to ISF, if the ball is hit to the outfield, and there is a play at first, the runner must use the orange base.