Duck blocks way in bar (3)
I believe the answer is:
rod
'bar' is the definition.
(I've seen this before)
'duck blocks way' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'blocks' means one lot of letters goes inside another (the inside letters form a 'blockage').
'way' becomes 'rd' (short for road).
'o' going inside 'rd' is 'ROD'.
'in' acts as a link.
(Other definitions for rod that I've seen before include "Sceptre" , "Flexible stick for 11 Down" , "Instrument of punishment" , "A few yards" , "Measurement" .)