Incidental contact

Have you ever NOT called a foul on the defense when a defender trips the opposing player dribbling the ball. I had a call recently where the offensive player (girls) was running down court and the defender was not really putting any pressure on her and their legs got tangled and the offensive player stumbled and lost possession. I passed on the potential foul, because I felt it was simply incidental contact. I was just wondering if any of you ever made an interpretation like this or do you automatically call that a foul on the defense.