Charlie, leaping initially into bed (4)
I believe the answer is:
clot
'charlie' is the definition.
(both can mean a foolish person)
'leaping initially into bed' is the wordplay.
'initially' says to take the initial letters.
'into' is an insertion indicator.
'bed' becomes 'cot' (cot is a kind of bed).
The first letter of 'leaping' is 'l'.
'l' going into 'cot' is 'CLOT'.
(Other definitions for clot that I've seen before include "Curdle - idiot" , "Thrombus - fool" , "Mass of material" , "Small lump of blood or other liquid" , "Semi-solid mass -- dunce" .)