Bob turns terribly inflexible (8)
I believe the answer is:
stubborn
'inflexible' is the definition.
(I've seen this before)
'bob turns terribly' is the wordplay.
'terribly' indicates anagramming the letters.
'bob'+'turns'='bobturns'
'bobturns' with letters rearranged gives 'STUBBORN'.
(Other definitions for stubborn that I've seen before include "hard to bend" , "Obstinate, bullheaded" , "Showing dogged determination" , "Resistant to change" , "Wilful" .)