Extremely ironic, my terms badly affecting both sides (9)
I believe the answer is:
symmetric
'affecting both sides' is the definition.
'extremely ironic my terms badly' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'badly' is an anagram indicator.
'ironic' with its centre removed is 'ic'.
'ic'+'my'+'terms'='icmyterms'
'icmyterms' is an anagram of 'SYMMETRIC'.
(Other definitions for symmetric that I've seen before include "Equally balanced" , "Regular" .)