Inflexible — read nothing but rubbish (8)
I believe the answer is:
obdurate
'inflexible' is the definition.
(I've seen this before)
'read nothing but rubbish' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'rubbish' indicates an anagram (a poor quality or rubbish spelling of the letters).
'read'+'o'+'but'='readobut'
'readobut' is an anagram of 'OBDURATE'.
(Other definitions for obdurate that I've seen before include "Unyielding - cruel" , "Stubborn, unpersuadable" , "A doubter being stubborn" , "Dogged" , "Stiff-necked" .)