Lectures this person's held in markets (7)
I believe the answer is:
tirades
'lectures' is the definition.
(a tirade is an angry rant or lecture)
'this person's held in markets' is the wordplay.
'this person' becomes 'I'.
'held in' is an insertion indicator.
'markets' becomes 'trades'.
'i' inserted inside 'trades' is 'TIRADES'.
(Other definitions for tirades that I've seen before include "It dares to unleash long angry speeches" , "Speeches of violent denunciation" , "Rants" , "Abusive words" , "Denunciations" .)