FLY BALL STRIKING TOP OF OUTFIELD WALL
Rule 5.05(a):
Unless provided otherwise by local ground rule, a fair fly ball striking the top of the outfield wall and bounding back onto the playing field shall be treated the same as a fair fly ball that strikes the outfield wall and rebounds back onto the playing field (in play but may not be caught for the purposes of an out).
Unless provided otherwise by local ground rule, a fair fly ball striking the top of the outfield wall and bounding over the wall shall be ruled a home run.
Unless provided otherwise by a local ground rule, a fair fly ball striking the top of the outfield wall and remaining on the top of the wall shall be deemed a ground-rule double.
Unless provided otherwise by local ground rule, a fair fly ball striking the top of the outfield wall that in the umpire’s judgment would have bounded over the wall if not for the permissible action of a spectator shall be ruled a home run. A fair fly ball that strikes the top of the outfield wall and is picked up by a spectator while still in motion shall also be ruled a home run. A fair fly ball that lands on the top of the outfield wall and is picked up by a spectator after coming to a stop shall be deemed a ground-rule double.