Exact retribution for Geneva explosion (6)
I believe the answer is:
avenge
'exact retribution for' is the definition.
(to avenge is to get retribution for something)
'geneva explosion' is the wordplay.
'explosion' is an anagram indicator.
'geneva' anagrammed gives 'AVENGE'.
(Other definitions for avenge that I've seen before include "Exact reparation for a wrong" , "Even the score" , "Inflict harm in return (for wrong)" , "Take satisfaction for injury or wrong" , "Redress, vindicate" .)