flagwise

Then, with frequent backward glances over one shoulder, Jan lay down to his task, and, followed by Punch and the Master, began to fly over the springy turf with occasional short bays, his powerful tail waving flagwise over his haunches.

Jan A Dog and a Romance 1912

I saw that he had so loosed it that it lay flagwise on his shoulder.

Actions and Reactions Rudyard Kipling 1900

Sitting side by side husband and wife watched, with feelings that had little in common, the receding quay, Mary fluttering her damp handkerchief till the separate figures had merged in one dark mass, and even Tilly, planted in front, her handkerchief tied flagwise to the top of Jerry’s cane, could no longer be distinguished from the rest.

Australia Felix 2003