Grenade tossed over line blew up (8)
I believe the answer is:
enlarged
'blew up' is the definition.
('enlarge' can be a synonym of 'blow up')
'grenade tossed over line' is the wordplay.
'tossed' indicates anagramming the letters.
'over' means one lot of letters goes inside another.
'line' becomes 'l'.
'grenade' is an anagram of 'enarged'.
'enarged' placed around 'l' is 'ENLARGED'.
(Other definitions for enlarged that I've seen before include "Made bigger like photo" , "Expanded, amplified" , "Magnified" , "Made bigger, say photo" , "Increased, augmented" .)