fair/foul

Question
The field is not enclosed, one of the many you find at any park, where the fenceline ends about 10-15 feet after 1st and 3rd base with a height of 10 feet or more.
Question: If a pop fly is caught that carries over the top of the fence while the third or first basemen still has both feet on the playing surface while reaching on the other side of the fence - is this an out?
In any other instance would the "catch and carry" in youth baseball be enforced.
Same scenario in Major leagues - Catcher catches a pop-up while reaching around the up and down fence directly behind home plate

Answer
You can reach into a dead ball area and make a catch for an out.  The only restriction for the out to count is that one foot must come down in live ball territory after the catch.  If the player can't get one foot down in live ball territory, then the play would just be a foul ball.  As for catch and carry, if the player makes the catch and then runs into dead ball territory, that would be a catch and carry situation and all runners are allowed to advance 2 based from the time of pitch.  I hope this answers you question.