Rugby team, very loud, surrounding one youngster (7)
I believe the answer is:
fifteen
'rugby team' is the definition.
(a rugby union team has 15 players)
'loud surrounding one youngster' is the wordplay.
'loud' becomes 'ff' (musical abbreviation for fortissimo, very loud).
'surrounding' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'youngster' becomes 'teen' (teenager).
'ff' enclosing 'i' is 'fif'.
'fif'+'teen'='FIFTEEN'
'very' is the link.
(Other definitions for fifteen that I've seen before include "Square root of two hundred and twenty-five" , "... number" , "Product of two primes" , "/8 across Today's milestone. That's a lot of Simplex crosswords" , "Square root of 225" .)