Deer stops one in performance (2,5)
I believe the answer is:
on stage
'performance' is the definition.
(I've seen this before)
'deer stops one' is the wordplay.
'deer' becomes 'stag' (stag is a kind of deer).
'stops' is an insertion indicator (stopping can mean blocking a gap).
'stag' placed within 'one' is 'ON-STAGE'.
'in' is the link.
(Other definitions for on stage that I've seen before include "Performing" , "in front of a audience" , "playing a part?" , "visible to audience" , "like passengers in Wild West" .)