Reinforce smooth catch (7)
I believe the answer is:
sandbag
'reinforce' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Perhaps you can see a link between them that I don't see?
'smooth catch' is the wordplay.
'smooth' becomes 'sand' (sanding is a kind of smoothing).
'catch' becomes 'bag' (synonyms).
'sand'+'bag'='SANDBAG'
Can you help me to learn more?
(Other definitions for sandbag that I've seen before include "Flood barrier builder" , "heavy weight" , "defensive article" , "One piled for flood protection" , "Flood defence" .)