Witness defending African party, spirited gathering? (6)
I believe the answer is:
seance
'spirited gathering?' is the definition.
(gathering for communicating with spirits)
'witness defending african party' is the wordplay.
'witness' becomes 'see' (synonyms).
'defending' is an insertion indicator.
'african party' becomes 'anc' (African National Congress, South African party).
'see' going around 'anc' is 'SEANCE'.
(Other definitions for seance that I've seen before include "Medium's meeting" , "Spiritualist meeting presided over by medium" , "Spiritualist meeting chaired by medium" , "Spirit meeting" , "spirited meeting" .)