Old hat only brought in to be re-blocked (8)
I believe the answer is:
obsolete
'old hat' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for obsolete that I've seen before include "Outmoded, passe" , "No longer current" , "Boots eel away, being out of date" , "Pass" , "Dead" .)