Selection of people: four originally darn trousers (5)
I believe the answer is:
draft
'selection of people' is the definition.
(process of selecting sports players)
'four originally darn trousers' is the wordplay.
'originally' says to take the initial letters.
'darn' becomes 'drat' (both are mild expletives).
'trousers' is an insertion indicator (to trouser can mean to contain or hold).
The initial letter of 'four' is 'f'.
'f' put into 'drat' is 'DRAFT'.
(Other definitions for draft that I've seen before include "Outline or sketch" , "Formulate" , "Rough sketch" , "Rough drawing" , "Draw an outline" .)