Reporting to fix support (8)
I believe the answer is:
underpin
'support' is the definition.
(underpinning is a kind of supporting)
'reporting to fix' is the wordplay.
'reporting to' becomes 'under'.
'fix' becomes 'pin' (pinning is a kind of fixing**).
'under'+'pin'='UNDERPIN'
(Other definitions for underpin that I've seen before include "Support or strengthen from beneath" , "buttress" , "Form the basis for" , "Prop up with nun pride" , "corroborate" .)