The poem begins in midair, so to speak—immediately diving into its extended metaphor of the poet as an acrobat. The reader doesn't arrive at the main clause of the poem's winding opening sentence until line 6, however; until then, they'd be forgiven for thinking the poem was about an actual acrobat.
Such a performer is, indeed, risking death when doing tricks up in the air, "above the heads / of his audience." And by "risking absurdity," the speaker means that this performer is in danger of looking ridiculous. Once readers know that the poem is actually using all this acrobat imagery to talk about the process of writing poetry, these lines take on a different meaning. The poet is always at risk of looking like a fool or even metaphorically dying (perhaps in the sense of their work being such a failure that they're forgotten).
The poem's winding syntax (or arrangement of words) and use of enjambment create an immediate sense of momentum and anticipation, breathlessly pulling the reader down the page and perhaps even evoking the tension one might feel while watching a trapeze artist perform.
The complete lack of punctuation allows these lines to flow freely, without obstruction. The poem also plays with white space, indenting lines far from the left-hand margin. All this space reflects the image of a figure performing up in the air, surrounded by empty space.
While the poem is visually striking, the speaker also plays with sound to great effect. Note all the sharp /k/ and /t/ consonance and hissing sibilance in line 1, for example:
Constantly risking absurdity
The line feels crisp and clear, but also slippery because of that /s/. The sounds of the line evoke the way both the poet and the acrobat must strike a balance or else "fall" into "absurdity."