Tug, small, for US nationals (5)
I believe the answer is:
yanks
'us nationals' is the definition.
(Yank can informally mean an American)
'tug small' is the wordplay.
'tug' becomes 'yank' (both can mean to pull).
'small' becomes 's' (abbreviation - e.g. clothes size).
'yank'+'s'='YANKS'
'for' is the link.
(Other definitions for yanks that I've seen before include "Pulls sharply" , "Physical jerks" , "Tugs" , "Americans; pulls" .)