Drain power during strike (7)
I believe the answer is:
deplete
'drain' is the definition.
(thesaurus)
'power during strike' is the wordplay.
'power' becomes 'p'.
'during' is an insertion indicator.
'strike' becomes 'delete'.
'p' placed into 'delete' is 'DEPLETE'.
(Other definitions for deplete that I've seen before include "Run down (e.g. stocks)" , "Reduce (stocks)" , "Use up quantities of, reduce store" , "Drain" , "Use up, reduce in quantity" .)