Ball hit towards third base strikes edge of base facing home plate pops up and lands a few feet foul about 10 ft behind third base. (not touched by fielder until lands in foul territory.
IMU that whether or not this ball is fair depends on where it crosses the foul line. if it crossed the foul line after passing the back edge(furthest from home plate) of 3B then it is a fair ball, if it crosses the foul line before it crosses the back edge of 3B it's foul.
I have a friend who insists it's fair ball either way.