Ah, but if you can define it, it is not Zen.
Which can probably be beautifully written in Japanese, and less well in our brutish amalgam of anglo-saxon and old norman french.
Japanese archery (kyu-do, IIRC) takes as a premise that it is the art of shooting arrows without (the effort of) shooting them. Which is the product of a great deal of concentration, and thousands of repetitions.
A person who applies concentration and thousands of repetitions to any task will built up a "muscle memory" which, if allowed, frees up some portion of that person's perception. That freed-up perception will notice/focus upon new or previously unseen things.
In shooting, when you get to the point that the sight alignment is automatic; the front sight mostly a blur, you can "see" all sorts of other things going on.
This, from not being "busy" with the "Uh, there's the rear sight, where's the front sight; oh, it's to the left; where's the target now; wait, the sight is not aligned; shoot, this thing dances around a lot; where'd that sight go again" sort of hectic process.
Instead, it's
"Target in sight; draw; weapon comes up--note the mirage, is that a shadow on the target, etc.; arms and weapon come up; sights come on target; SHOT; see target, examine peripheral vision; see hole in target; repeat."
Or words to that effect, since no mere words can describe the sound of one hand clapping.