Influence rascal to do something (6)
I believe the answer is:
impact
'influence' is the definition.
(I know that impact is a type of influence)
'rascal to do something' is the wordplay.
'rascal' becomes 'imp' (synonyms).
'to' is a charade indicator (letters next to each other).
'do something' becomes 'act' (to act is to do something).
'imp'+'act'='IMPACT'
(Other definitions for impact that I've seen before include "Serious effect" , "Strong effect" , "Collision - effect" , "Repercussions" , "Forceful contact between two objects" .)