Tugs in yard are new, Kelvin beginning to say (5)
I believe the answer is:
yanks
'tugs' is the definition.
(I've seen this in another clue)
'yard are new kelvin beginning to say' is the wordplay.
'yard' becomes 'y' (abbreviation).
'are' becomes 'a' (short for 'are', historical unit of measurement).
'new' becomes 'n' (abbreviation as in New Testament NT).
'kelvin' becomes 'K' (abbreviation for the unit of temperature).
'beginning to' suggests taking the first letters.
The initial letter of 'say' is 's'.
'y'+'a'+'n'+'k'+'s'='YANKS'
'in' is the link.
(Other definitions for yanks that I've seen before include "Tugs" , "Americans; pulls" , "Pulls sharply" , "Physical jerks" .)