Fellow, terribly fit, getting directions and quantity (7)
I believe the answer is:
fifteen
'quantity' is the definition.
(fifteen is a kind of quantity)
'fellow terribly fit getting directions and' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'terribly' indicates an anagram.
'getting' means one lot of letters go next to another.
'directions' becomes 'ee' (the abbreviation for east written twice).
'and' becomes 'n' (common abbreviation for 'and').
'fit' anagrammed gives 'ift'.
'f'+'ift'+'ee'+'n'='FIFTEEN'
(Other definitions for fifteen that I've seen before include "Square root of 225" , "Rugby Union team" , "Square root of two hundred and twenty-five" , "... number" , "Film type" .)