Old man introduced to partners for bridge (4)
I believe the answer is:
span
'bridge' is the definition.
('span' can be a synonym of 'bridge')
'old man introduced to partners' is the wordplay.
'old man' becomes 'pa' (both can mean father).
'introduced to' indicates putting letters inside.
'partners' becomes 'sn'.
'pa' going within 'sn' is 'SPAN'.
'for' acts as a link.
(Other definitions for span that I've seen before include "Complete duration" , "Bridge - rotated" , "Bridge made of pans" , "Go across" , "too short for the foot" .)