Part of goal is to thwart lawyers (8)
I believe the answer is:
crossbar
'part of goal' is the definition.
('crossbar' is part of 'goal')
'thwart lawyers' is the wordplay.
'thwart' becomes 'cross' ('cross' can be a synonym of 'thwart').
'lawyers' becomes 'bar' (I've seen this before).
'cross'+'bar'='CROSSBAR'
'is to' is the link.
(Other definitions for crossbar that I've seen before include "Horizontal piece, on a bicycle say" , "one's seen on a bike?" , "Bit of sports equipment" , "Post connecting goalposts" , "Part of bicycle or goal" .)