Holds up part of theatre (6)
I believe the answer is:
stalls
I believe this is a double definition.
'holds up' is the first definition.
(stall can mean to delay or hold up)
'part of theatre' is the second definition.
(seats in a theatre)
(Other definitions for stalls that I've seen before include "Stops; theatre seats" , "Posh seats in the theatre" , "Uses delaying tactics to gain time" , "pews" , "Cuts out in parterre?" .)