To expel Open University student leaders ... (4)
I believe the answer is:
oust
'to expel' is the definition.
('oust' can be a synonym of 'expel')
'open university student leaders' is the wordplay.
'open university' becomes 'OU'.
'student leaders' becomes 'st' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ou'+'st'='OUST'
Can you help me to learn more?
(Other definitions for oust that I've seen before include "Remove from a position of power" , "Overthrow" , "kick out" , "Depose" , "Turn out" .)