Head off from party, cycling plastered essentially (5)
I believe the answer is:
avert
'head off' is the definition.
(both can mean to prevent)
'party cycling plastered essentially' is the wordplay.
'party cycling' becomes 'aver' (I am not sure about this - if you are sure you should believe this answer much more).
'essentially' means to look at the middle letters.
The centre of 'plastered' is 't'.
'aver'+'t'='AVERT'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for avert that I've seen before include "Obviate" , "Forestall" , "Turn away or aside" , "Turn away, prevent" , "Deflect away" .)