Flog lad regularly, resulting in collapse (4)
I believe the answer is:
fold
'collapse' is the definition.
(thesaurus)
'flog lad regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'flog'+'lad'='floglad'
The alternate letters of 'floglad' are 'FOLD'.
'resulting in' acts as a link.
(Other definitions for fold that I've seen before include "Bend over; pen" , "Cease trading" , "Congregation; (firm) go bankrupt" , "Prepare pages to put in small envelope" , "Crease" .)