Provide what's lacking when the referee gets sick (6)
I believe the answer is:
refill
'provide what's lacking when' is the definition.
I can't judge whether this defines the answer.
'referee gets sick' is the wordplay.
'referee' becomes 'ref' (synonyms).
'gets' is a charade indicator (letters next to each other).
'sick' becomes 'ill' (synonyms).
'ref'+'ill'='REFILL'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for refill that I've seen before include "Replace contents" , "Another drink" , "Another cuppa perhaps" , "Charge again" , "Solution for dried-up writer" .)