To express disapproval of Mike leads to explosion (4)
I believe the answer is:
boom
'explosion' is the definition.
(thesaurus)
'to express disapproval of mike leads' is the wordplay.
'to express disapproval of' becomes 'boo' (I've seen this before).
'leads' indicates taking the first letters.
The first letter of 'mike' is 'm'.
'boo'+'m'='BOOM'
'to' acts as a link.
(Other definitions for boom that I've seen before include "Time of great prosperity - hear the sound" , "When business is great, opposite to bust" , "Deep and resonant sound" , "Deep hollow sound" , "Bonanza; roar" .)