What the police had on his hair? (3)
I believe the answer is:
oil
'what the police had on his hair?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'on his hair?' is the wordplay.
'on' becomes 'o' (I've seen this in other clues).
'his hair?' becomes 'il' (I am not sure about this - if you are sure you should believe this answer much more).
'o'+'il'='OIL'
Can you help me to learn more?
(Other definitions for oil that I've seen before include "what can be seen on iceberg" , "Lubricate; fuel" , "painting" , "Liquid fuel" , "Fossil fuel" .)