Reinforce broken lobster (7)
I believe the answer is:
bolster
'reinforce' is the definition.
(bolstering is a kind of reinforcing)
'broken lobster' is the wordplay.
'broken' indicates an anagram.
'lobster' with letters rearranged gives 'BOLSTER'.
(Other definitions for bolster that I've seen before include "Long thick pillow" , "Shore up" , "Extended pillow" , "Support; long pillow" , "support for head after retiring" .)