Slack adjustment creates deficiencies (5)
I believe the answer is:
lacks
'deficiencies' is the definition.
('lack' can be a synonym of 'deficiency')
'slack adjustment' is the wordplay.
'adjustment' is an anagram indicator.
'slack' anagrammed gives 'LACKS'.
'creates' acts as a link.
(Other definitions for lacks that I've seen before include "Wants, is deficient in" , "Is without, wants" , "Has a want" , "Doesn't have" , "Needs" .)