Steep change by the first group (6)
I believe the answer is:
septet
'group' is the definition.
(I know that septet is a type of group)
'steep change by the first' is the wordplay.
'change' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'the first' becomes 't' (1st letter of 'the').
'steep' with letters rearranged gives 'septe'.
'septe'+'t'='SEPTET'
(Other definitions for septet that I've seen before include "Music piece for seven" , "Odd number of players performing" , "Musical group" , "Band of seven players" , "Seven-piece band" .)