'Clash' group's approaching start of gig (5)
I believe the answer is:
Here is my best explanation:
'clash' is the definition.
('clang' can be a synonym of 'clash')
'group's approaching start of gig' is the wordplay.
'group' becomes 'clan' (clan is a kind of group**).
'approaching' is a charade indicator (letters next to each other).
'start of' says to take the initial letters.
The first letter of 'gig' is 'g'.
(Other definitions for clang that I've seen before include "Noise as of cymbals", "Noise from crane", "Toll of a bell", "Loud resonant noise", "The sound of metal on metal", "Jangle", "Metallic sound", "Metallic noise", "A loud ringing sound" and "Resonant metallic sound".)