With a single blow, it's possibly beaten! (3)
I believe the answer is:
rap
'blow it's possibly beaten' is the definition.
I can't tell whether this defines the answer.
'with a single' is the wordplay.
'with' means one lot of letters goes inside another.
'single' becomes 'rp' (I am not sure about this - if you are sure you should believe this answer much more).
'a' inserted into 'rp' is 'RAP'.
Can you help me to learn more?
(Other definitions for rap that I've seen before include "Administer sharp blow, being below par" , "talking during musical performance" , "Rhyming monologue recited to rock music below par" , "Sharply criticise" , "Sharp knock; rebuke" .)