Maybe Paul McCartney’s No 1 for Beatles — Help! (7)
I believe the answer is:
bassist
'maybe paul mccartney's no 1' is the definition.
I can't tell whether this definition defines the answer.
'beatles help' is the wordplay.
'beatles' becomes 'b' (this might be a standard abbreviation I've not previously seen).
'help' becomes 'assist' (to assist someone is to help them).
'b'+'assist'='BASSIST'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for bassist that I've seen before include "jazz player" , "Musician" .)