Sport in Middle-Earth

[The Saucepan Man]

Banners depicting the emblems of realms are displayed in LotR in situations other than battle. From The Field of Cormallen:

And so the red blood rushing in their faces and their eyes shining with wonder, Frodo and Sam went forward and saw amidst the clamorous host were set three high-seats built of green turves. Behind the seat upon the right floated, white on green, a great horse running free; upon the left was a banner, silver upon blue, a ship swan-prowed faring on the sea; but behind the highest throne in the midst of all a great standard spread in the breeze, and there a white tree flowered upon a sable field beneath a shining crown and seven glittering stars.

And mounted upon Saucepan's car, red upon white, floated the cross of St George.

I see nothing wrong in displaying my national flag as a symbol of my pride in my country and to show my support for my national team on sporting occasions (it is mounted on the car's aerial, thus presenting no driving hazard). Personally, I think that the cross of St George is an extremely attractive device and I am proud to fly it. And, if it has "nationalistic" connotations, then I am happy to reclaim it on behalf of all who take pride in their country, while maintaining admiration and respect for other nations.