Transport prisoner, extremely volatile at end of day (6)
I believe the answer is:
convey
'transport' is the definition.
(conveying is a kind of transporting)
'prisoner extremely volatile at end of day' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'extremely' says to hollow out the word (remove centre letters).
'at end of' suggests the final letters.
'volatile' with its centre taken out is 've'.
The last letter of 'day' is 'y'.
'con'+'ve'+'y'='CONVEY'
(Other definitions for convey that I've seen before include "Transport or transmit" , "Make known -- pass on" , "Pass on or transport" , "Carry from one place to another" , "Transport; communicate" .)