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This shot answers our question about what we were seeing here: a sort of cloth plume attached to the point of the Knight of Flower’s ornate helmet. Highly impressive.
Doc, who’s been an extra on the show, identifies the banner in the upper left as featuring three bull moose heads, which seems like it’s the show’s interpretation of the House Hornwood arms. Perhaps some Hornwood lance followed along with Lord Stark, or perhaps there’s a Hornwood man among his guard who’s chosen to take part (three of Ned’s guardsmen, including Jory, opted to ride in the tourney in the books). To the right end, we see another banner, which is clearly the shows take on the Tyrell arms. The field is a very pale green.