Fair or Foul?

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Had a situation the other day I've never seen before. Outs, organization etc., make no difference. Batter hits a pop fly down 3rd base line. Ball hits ground just beyond 3rd base (about 2 or 3 feet), spins backwards and passes 3rd base rolling towards home and toward foul line. Ball ends up settling in foul territory. No one touches ball. Umpires don't call foul ball. Ball is eventually picked up with no plays anywhere.

Discussion starts. Ball was fair, it went "PAST" 3rd base before it went foul. Other argument was, ball wasn't touched, makes no difference where it first hit, it ended up going foul in front of 3rd base. Ball is foul.

Decision was, it was a fair ball.

What's the call? I read the ASA rules and nothing really jumped out in helping determine this call.