MLB Rule: Home Run When Outfielder Falls Over Fence?

Question
In major league baseball, if an outfielder catches a fair fly ball and falls over the outfield fence, is that considered an out or because his momentum carried him over the wall, would that be a home run? Neither the player nor the ball when caught, remain in the playing field

Answer
Devin,
I looked through the MLB rule book and I can't find anything.  I am sorry I cannot give you an accurate answers.  I can make a guess but I can only answer a question that I am absolutely certain about.  I have never been in or have seen this situation.  There are some umpires in the all experts baseball instruction section that could answer your question.

Thank You,
John Priest