It may bulge unless keeper makes clear catch! (3)
I believe the answer is:
net
'catch' is the definition.
(net can mean to catch)
'it may bulge unless keeper makes clear' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
The remaining letters 'ne' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for net that I've seen before include "Meshwork" , "Score a goal" , "It's see-through" , "Catch, ensnare" , "Mesh; after tax" .)