Regarding a hackneyed piece in G (5)
I believe the answer is:
eying
'regarding' is the definition.
The answer and definition can be both to do with perception as well as being present participle verbs.
Maybe there's an association between them I don't understand?
'a hackneyed piece in g' is the wordplay.
'a hackneyed piece' becomes 'ey' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ey'+'in'+'g'='EYING'
Can you help me to learn more?
(Other definitions for eying that I've seen before include "Observing" , "Looking at with interest" , "Watching closely" , "Ogling," , "In the process of close scrutiny" .)