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 "Keen perception", "Mental sharpness as in business", "Shrewdness, good for business", "Insightfulness", "Ability to take well judged decisions", "'Keenness, depth of perception (6)'", "Ability to judge and decide quickly", "Cleverness in business", "Shrewdness, intelligence in business" and "Good judgment".)