A lot of anger among most of selected singers (6)
I believe the answer is:
choirs
'singers' is the definition.
'a lot of anger among most of selected' is the wordplay.
'a lot of' means to remove the last letter (most of the word but not all of it).
'anger' becomes 'ire' (ire is intense rage).
'among' indicates putting letters inside (inserted letters are placed among others).
'most of' means to remove the last letter.
'selected' becomes 'chose' ('choose' can be a synonym of 'select').
'ire' with its final letter removed is 'ir'.
'chose' with its last letter removed is 'chos'.
'ir' going inside 'chos' is 'CHOIRS'.
(Other definitions for choirs that I've seen before include "Groups of singers, often in churches" , "Bands of singers" , "Singing teams" , "Singing groups" , "Groups of singers, in church say" .)