Perhaps with birds of prey, you might have a “fowl swoop.” Perhaps with gangly young basketball players, you might have a “foul swoop.” But when you’re looking for what to call a sudden, swift action, “fell swoop” is the correct form. How many of you are writing this one right?
You can blame Shakespeare for the confusion. His use of “fell swoop” utilizes an old form of “fell,” which means “savage” or “ruthless” (as in “felony”), but the exact line in Macbeth where he uses it does also mention chickens. Fell. Fowl. Writer foul?
What do you think?