CID officers placed last in the contest (7)
I believe the answer is:
dispute
'contest' is the definition.
(I know that dispute is a kind of contest)
'cid officers placed last in the' is the wordplay.
'cid officers' becomes 'dis' (I can't explain this - if you can you should give a lot more credence to this answer).
'placed' becomes 'put' (I've seen this before).
'last in' says to take the final letters.
The last letter of 'the' is 'e'.
'dis'+'put'+'e'='DISPUTE'
Can you help me to learn more?
(Other definitions for dispute that I've seen before include "Question or deny accuracy or validity" , "Altercation" , "Argue about (something)" , "Row" , "Disagree or challenge" .)