Weak start of cheer from party official (4)
I believe the answer is:
whip
'party official' is the definition.
(I've seen this before)
'weak start of cheer' is the wordplay.
'weak' becomes 'w' (physics symbol as in W-boson).
'start of cheer' becomes 'hip' (I can't justify this - if you can you should give a lot more credence to this answer).
'w'+'hip'='WHIP'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for whip that I've seen before include "Disciplinary object or official" , "MP enforcing discipline" , "Flagellate" , "Pudding" , "Steal - something to hit people with" .)