Performing with two legs (2,5)
I believe the answer is:
on stage
'performing' is the definition.
(I've seen this before)
'with two legs' is the wordplay.
'two legs' means two replacements for 'leg'.
'with' means one lot of letters go next to another.
'leg' becomes 'on' (cricket term, fielding positions).
'leg' becomes 'stage' ('stage' can be a synonym of 'leg').
'on' next to 'stage' is 'ON-STAGE'.
(Other definitions for on stage that I've seen before include "Acting" , "playing a part?" , "like passengers in Wild West" , "visible to audience" , "performance" .)