Almost overwhelm gang? That's shocking (8)
I believe the answer is:
flooring
'shocking' is the definition.
('floor' can be a synonym of 'shock')
'almost overwhelm gang?' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'overwhelm' becomes 'floor' (I've seen this in another clue).
'gang?' becomes 'ring' (synonyms).
'floor' with its last letter taken off is 'floo'.
'floo'+'ring'='FLOORING'
'that's' acts as a link.
(Other definitions for flooring that I've seen before include "Bewildering" , "Carpet or lino, say" , "Baffling completely, knocking down" , "Material for walking on" , "Carpet, wood, etc." .)