Influence rascal with performance (6)
I believe the answer is:
impact
'influence' is the definition.
(impact is a kind of influence)
'rascal with performance' is the wordplay.
'rascal' becomes 'imp' ('imp' can be a synonym of 'rascal').
'with' means one lot of letters go next to another.
'performance' becomes 'act' (act is a kind of performance).
'imp'+'act'='IMPACT'
(Other definitions for impact that I've seen before include "The striking of one body against another" , "Force of colllision or blow" , "Force of blow or collision" , "Marked effect; hit" , "Forceful consequence" .)