There are farms in Ireland on both sides of the border. Imagine kicking your GAA ball over to the other side of the garden and you switch countries. A smugglers paradise over the last 100 years.
What's a GAA ball?
It's a ball belonging to Irelands most popular sport. One of the native games of the country. The Gaelic Athletic Association.
I assume he means a Gaelic football. Gaelic football is governed by the Gaelic Athletic Association along with Hurling and Gaelic Handball.
I think remembering something like that in Hannah Arendt's biography, but I couldn't tell more... Maybe something about leaving Germany by leaving an house through such a door in the opposite side.