Pressing part of leg nipped by boxer (7)
I believe the answer is:
pushing
'pressing' is the definition.
(pushing is a kind of pressing)
'leg nipped by boxer' is the wordplay.
I cannot quite see how this works, but
'leg' could be 'shin' (I have seen 'Lower leg ' mean 'shin' so perhaps 'leg' could also mean 'shin') and 'shin' is located in the answer.
'boxer' could be 'pug' (short for pugilist - term for boxer) and 'pug' is found within the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'part of' is the link.
Can you help me to learn more?
(Other definitions for pushing that I've seen before include "Shoving" , "Enterprising" , "Pressing against" .)