Worry is stopping a good individual (7)
I believe the answer is:
agonise
'worry' is the definition.
(to agonise is to worry or fret)
'is stopping a good individual' is the wordplay.
'stopping' means one lot of letters goes inside another (inserted letters stop or plug a gap).
'good' becomes 'g' (abbreviation).
'individual' becomes 'one' (an individual is one person).
'a'+'g'+'one'='agone'
'is' inserted within 'agone' is 'AGONISE'.
(Other definitions for agonise that I've seen before include "Fret, worry inordinately" , "Be in torments of indecision" , "Worry greatly (over something); I go sane (anag.)" , "Worry intensely" , "Struggle mentally" .)