Former boundary broken by Newton, practical scientist (12)
I believe the answer is:
experimenter
'scientist' is the definition.
(experimenter is a kind of scientist)
'former boundary broken by newton practical' is the wordplay.
I cannot quite understand how this works, but
'former' could be 'ex' (prefix meaning former or onetime) and 'ex' is found in the answer.
'boundary' could be 'rim' (rim is a kind of boundary) and 'rim' is present in the answer.
'newton' could be 'n' (symbol for the scientific unit of force) and 'n' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for experimenter that I've seen before include "Scientist" , "lab worker?" .)