Fanatical, starts to rail against broadsheet papers (5)
I believe the answer is:
rabid
'fanatical' is the definition.
(I know that fanatical can be written as rabid)
'starts to rail against broadsheet papers' is the wordplay.
'starts to' says to take the initial letters.
'papers' becomes 'ID' (identification papers).
The initial letters of 'rail against broadsheet' is 'rab'.
'rab'+'id'='RABID'
(Other definitions for rabid that I've seen before include "Affected by hydrophobia" , "Extremely fanatical" , "Extreme, fanatical" , "Affected by 24 across" , "Mad; raging" .)