In terms of grabbing an easy out, they don’t come much easier than this one:
A common rule myth is that home plate is in foul territory (it is not) or a ball that strikes home plate is foul (it is not) or finally a ball that hits behind home plate is foul (it is not).
If a batter hits the ball down the line and half way between third and home it rolls fair, this is a fair ball. Hitting the ball behind the plate is no different.
If the ball has not crossed first or third, the call is made by where the ball (not fielder) is when the ball is touched or where the ball comes to rest.
Nice job by the umpire in not killing this play too soon.
Page 37 of RuleGraphics covers fair/foul balls.