What Should be the Call?
 

ASA slow pitch softball rules.

Bases loaded 2 out. Line drive hits the runner who's standing on 3rd base...

What should be the call?

Probably foul - 'course that depends on "how" the runner is standing on 3B. Most will be with foot on the bag & the other in foul territory.

ASA Rule Supplement #44 (PG.130):
RUNNER HIT BY FAIR BATTED BALL
A." While In Contact With The Base A runner who is hit by a FAIR batted ball while in contact with the base should not be called out unless the act was is intentional. The ball remains live, or becomes immediately dead, depending on the closest defensive player. When the closest defensive player is in front of the base that the runner is in contact with, the ball remains live. However when the closest defensive player is behnd the base, the ball is dead. Should the ball be ruled dead and the batter awarded a base hit, only runners forced to advance because the batter was placed on first base shall advance one base."
B."While Not In Contact With The Base A runner who is hit by a FAIR batted ball while not in contact with the base should be called out or ruled safe depending on the interference rule."
Rule 8 Section 7 J&K or Rule 8 Section 8 D&F.

You asked what should the call be?

Steve has indicated what has to be decided first, then follow the rule supplement.

Then there is the Secret Squirrel Softball Syllabus.

1. What's the score?
1B. What's the inning.
2. How many games in a row is this for Blue?
3. What was the *****iness level of the players?

Depending upon the answers to 1 and 1B, Questions 2 & 3 may not be necessary.