I'm badly upset by such a drive (7)
I believe the answer is:
impetus
'such a drive' is the definition.
(impetus is a drive to do something)
'i'm badly upset by' is the wordplay.
'i'm' becomes 'im' ().
'badly' is an anagram indicator (letters in the wrong order).
'by' means one lot of letters go next to another.
'upset' anagrammed gives 'petus'.
'im'+'petus'='IMPETUS'
(Other definitions for impetus that I've seen before include "Motivation" , "Moving force" , "Driving force, forward movement" , "Thrust" , "Catalyst" .)