Leader in trade to study factory's boring routine (9)
I believe the answer is:
treadmill
'boring routine' is the definition.
(I've seen this before)
'leader in trade to study factory's' is the wordplay.
'leader in' indicates taking the first letters.
'to study' becomes 'read' (synonyms).
'factory' becomes 'mill' (mill is a type of factory).
The initial letter of 'trade' is 't'.
't'+'read'+'mill'='TREADMILL'
(Other definitions for treadmill that I've seen before include "Tiresome job" , "Dreary repetitive work" , "Monotonous routine work, as on wheel of old" , "day-to-day grind" , "Daily grind" .)