Has a poor work rate, but is left in the side, possibly (5)
I believe the answer is:
idles
'has a poor work rate but' is the definition.
I can't judge whether this definition defines the answer.
'left in the side possibly' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in the' is an insertion indicator.
'possibly' indicates an anagram.
'side' anagrammed gives 'ides'.
'l' inserted within 'ides' is 'IDLES'.
'is' is the link.
Can you help me to learn more?
(Other definitions for idles that I've seen before include "Spends time doing nothing" , "Lazes about, just ticks over" , "Does little, just ticks over" , "Of engine, just ticks over in neutral" , "Avoids working" .)