Sharpness of workers after a short reduction (6)
I believe the answer is:
Here is my best explanation:
'sharpness' is the definition.
'workers after a short reduction' is the subsidiary indication.
'workers' becomes 'men' (man is a kind of worker).
'after' says to put letters next to each other.
'short' means to remove the last letter.
'reduction' becomes 'cut' (cut is a kind of reduction).
'cut' with its final letter taken off is 'cu'.
'men' after 'acu' is 'acumen'.
'of' is the link.
(Other definitions for acumen that I've seen before include "intuition", "Good judgment", "Sagicity as in business", "Ability to judge and decide quickly", "Shrewdness, good for business", "Being sharp", "Sharpness, penetration, quickness of perception", "Shrewdness, sharpness of mind", "ability to make good judgements" and "Shrewdness, intelligence in business".)