Scientific discipline leading baker brought back to a US city (6)
I believe the answer is:
botany
'scientific discipline' is the definition.
(botany is a kind of scientific discipline)
'leading baker brought back to a us city' is the wordplay.
'leading' says to take the initial letters.
'brought back' is a reversal indicator.
'us city' becomes 'ny' (short for New York).
The initial letter of 'baker' is 'b'.
'to' reversed gives 'ot'.
'b'+'ot'+'a'+'ny'='BOTANY'
(Other definitions for botany that I've seen before include "Science of plant life" , "The scientific study of plants" , "plants growing in one area" , "Science of plants" , "Unlucky, doomed" .)