Lines in sonnet? There’s support for us in folio note (8)
I believe the answer is:
fourteen
'lines in sonnet?' is the definition.
(a sonnet has 14 lines)
'support for us in folio note' is the wordplay.
'support for us' becomes 'our tee' (golf tee belonging to us).
'in' means one lot of letters goes inside another.
'folio' becomes 'f' (publishing abbreviation).
'note' becomes 'n' (abbreviation).
'f'+'n'='fn'
'ourtee' put inside 'fn' is 'FOURTEEN'.
'there's' acts as a link.
(Other definitions for fourteen that I've seen before include "Pounds in a stone?" , "Number of lines in a sonnet" , "Fen route (anag)" , "XIV" .)