Catch with a right and knock out (4)
I believe the answer is:
trap
'catch' is the definition.
(trapping is a kind of catching)
'right and knock out' is the wordplay.
I cannot really see how this works, but
'right' could be 'r' (common abbreviation) and 'r' is present in the answer.
'knock' could be 'tap' (synonyms) and 'tap' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
'with a' is the link.
Can you help me to learn more?
(Other definitions for trap that I've seen before include "The Web" , "Device to catch prey" , "one would be ill advised to enter?" , "Kisser" , "Snare, ruse" .)