A bowman piercing old man in part of leg (7)
I believe the answer is:
patella
'part of leg' is the definition.
(I know that patella is part of knee joint)
'a bowman piercing old man' is the wordplay.
'bowman' becomes 'tell' (I can't justify this - if you can you should believe this answer much more).
'piercing' indicates putting letters inside (some letters pierce a hole in a word).
'old man' becomes 'pa' (both can mean someone's father).
'a'+'tell'='atell'
'atell' put inside 'pa' is 'PATELLA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for patella that I've seen before include "Joint cover" , "Kneecap (anatomy)" , "positioned on each knee" , "bit of body usually under trousers!" , "Knee bone" .)