Scowl as David, say, gets a fifty (6)
I believe the answer is:
glower
'scowl' is the definition.
(I've seen this before)
'david say gets a fifty' is the wordplay.
'david say' becomes 'gower' (I can't justify this - if you can you should believe this answer much more).
'gets' is an insertion indicator (gets can mean captures or absorbs).
'a fifty' becomes 'l' (roman numeral).
'gower' going around 'l' is 'GLOWER'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for glower that I've seen before include "Look hotly or angrily" , "Stare angrily, scowl" , "Fierce look" , "Look black" , "Stare fiercely" .)