Gently strike a girl – on the knee (7)
I believe the answer is:
patella
'knee' is the definition.
(I've seen this before)
'gently strike a girl on the' is the wordplay.
I cannot quite see how this works, but
'gently' could be 'p' (musical abbreviation for 'piano', softly) and 'p' is found within the answer.
'a' is within the answer.
'girl' could be 'ella' (girl's name) and 'ella' is found within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for patella that I've seen before include "The formal kneecap" , "positioned on each knee" , "showing a bit of leg" , "bit of body usually under trousers!" , "Knee bone" .)