Bad rash needs to be controlled (9)
I believe the answer is:
harnessed
'be controlled' is the definition.
(I've seen this before)
'bad rash needs' is the wordplay.
'bad' indicates an anagram.
'rash'+'needs'='rashneeds'
'rashneeds' with letters rearranged gives 'HARNESSED'.
'to' is the link.
(Other definitions for harnessed that I've seen before include "controlled" , "Prepared horse for journey" , "ready to draw" .)