Disturb son, out of bed, eating fish (5,2)
I believe the answer is:
shake up
'disturb' is the definition.
('shake up' can be a synonym of 'disturb')
'son out of bed eating fish' is the wordplay.
'son' becomes 's'.
'out of bed' becomes 'up' ('up' can be a synonym of 'out of bed').
'eating' is an insertion indicator.
'fish' becomes 'hake' (I've seen this before**).
's'+'up'='sup'
'sup' enclosing 'hake' is 'SHAKE-UP'.
(Other definitions for shake up that I've seen before include "Radical reorganization" , "Organize anew" , "Jolt" , "Drastic reorganisation" , "Shock" .)