Rock group members' initially short tempers (6)
I believe the answer is:
stones
'rock group members'' is the definition.
(members of the Rolling Stones)
'initially short tempers' is the wordplay.
'initially' says to take the initial letters.
'tempers' becomes 'tones' (both can mean temperaments or attitudes).
The first letter of 'short' is 's'.
's'+'tones'='STONES'
(Other definitions for stones that I've seen before include "Rolling rock group" , "pop group" , "Small pieces of rock" , "''Sticks and ...... may break my bones''" , "Rolling ones gather no moss, it's said" .)