Scientist argues really well at first in row (6)
I believe the answer is:
darwin
'scientist' is the definition.
(Darwin is an example)
'argues really well at first in row' is the wordplay.
'at first' says to take the initial letters.
'in' indicates putting letters inside.
'row' becomes 'din' (both can mean a loud disturbance).
The first letters of 'argues really well' is 'arw'.
'arw' inserted inside 'din' is 'DARWIN'.
(Other definitions for darwin that I've seen before include "He initiated the theory of evolution" , "He proposed the theory of evolution" , "Australia's northernmost state capital" , "Charles . . . . . ., author of 'The Origin of Species'" , "Strangely inward antipodean city" .)