Influences deeds involving very loud explosions, primarily (7)
I believe the answer is:
affects
'influences' is the definition.
(I've seen this before)
'deeds involving very loud explosions primarily' is the wordplay.
'deeds' becomes 'acts' (I've seen this before).
'involving' is an insertion indicator.
'very loud' becomes 'ff' (musical abbreviation).
'primarily' says to take the initial letters.
The first letter of 'explosions' is 'e'.
'ff'+'e'='ffe'
'acts' enclosing 'ffe' is 'AFFECTS'.
(Other definitions for affects that I've seen before include "Has an effect on" , "Makes a difference to" , "Bears upon" , "Influences" .)