Provide what is needed to react badly (5)
I believe the answer is:
cater
'provide what is needed' is the definition.
(I've seen this in another clue)
'react badly' is the wordplay.
'badly' is an anagram indicator.
'react' is an anagram of 'CATER'.
'to' is the link.
(Other definitions for cater that I've seen before include "... you'll see minister" , "Provide goods or services for" , "Supply food and drink" , "Make provision for" , "Provide what is needed or wanted" .)