Six-footer in religious group? (6)
I believe the answer is:
insect
'six-footer' is the definition.
(I've seen this before)
'in religious group?' is the wordplay.
'religious group?' becomes 'sect' (eg a religious sect).
'in'+'sect'='INSECT'
(Other definitions for insect that I've seen before include "Worker, possibly" , "Bug" , "Small air-breathing arthropod" , "Invertebrate, often winged" , "Small invertebrate arthropod" .)