Flock initially caused damage (5)
I believe the answer is:
charm
'flock' is the definition.
(I have seen 'Flock of goldfinches ' mean 'charm' so perhaps 'flock' could also mean 'charm')
'initially caused damage' is the wordplay.
'initially' says to take the initial letters.
'damage' becomes 'harm' ('harm' can be a synonym of 'damage'**).
The first letter of 'caused' is 'c'.
'c'+'harm'='CHARM'
(Other definitions for charm that I've seen before include "small ornament" , "Bewitch or delight" , "Power of fascination" , "Campaign to gain support and become more popular" , "Personal attractiveness and charisma" .)