Peeved group of lawyers that joins supporters on pitch (8)
I believe the answer is:
crossbar
'that joins supporters on pitch' is the definition.
(a crossbar is supported by two goalposts)
'peeved group of lawyers' is the wordplay.
'peeved' becomes 'cross' (I've seen this before).
'group of lawyers' becomes 'bar' (the bar can mean the legal profession).
'cross'+'bar'='CROSSBAR'
(Other definitions for crossbar that I've seen before include "Horizontal part of a goal" , "It's over the goalie's head" , "Horizontal beam over goal posts" , "Top football goal" , "one's seen on a bike?" .)