Put up resistance after introduction of extremely shocking treatment (5)
I believe the answer is:
erect
'put up' is the definition.
(synonyms)
'resistance after introduction of extremely shocking treatment' is the wordplay.
'resistance' becomes 'r' (electronics abbreviation).
'after' means one lot of letters go next to another.
'introduction of' indicates taking the first letters.
'shocking treatment' becomes 'ect' (electro-convulsive therapy).
The initial letter of 'extremely' is 'e'.
'r' after 'e' is 'er'.
'er'+'ect'='ERECT'
(Other definitions for erect that I've seen before include "Build, set up" , "Build, put up" , "Crete (anag)" , "Build, upright" , "Not having a list" .)