Assumed, when one made a fuss (4,2)
I believe the answer is:
took on
'assumed' is the definition.
(I've seen this in another clue)
'when one made a fuss' is the wordplay.
I cannot really see how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is found within the answer.
The remaining letters 'took' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for took on that I've seen before include "Employed" , "challenged" , "Got upset < , did recruit" .)