A measure of pressure has rogue initially taking two steps back (6)
I believe the answer is:
pascal
'a measure of pressure' is the definition.
(I know that pascal measured physical quantity pressure)
'two steps back' is the wordplay.
'two steps' can mean two replacements for 'step'.
'step' becomes 'pas' (I've seen this before).
'step' becomes 'lac' (I can't explain this - if you can you should give a lot more credence to this answer).
'back' is a reversal indicator.
'lac' in reverse letter order is 'cal'.
'pas'+'cal'='PASCAL'
'has rogue initially taking' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for pascal that I've seen before include "clever thinker" , "Unit of pressure, French philosopher and programming language" , "religious philosopher" , "17th century French mathematician -- SI unit of pressure" , "Unit of pressure; French scientist" .)