Beasts getting one upset about a kiss (4)
I believe the answer is:
oxen
'beasts' is the definition.
(I have seen 'Beasts of burden ' mean 'oxen' so perhaps 'beasts' could also mean 'oxen')
'one upset about a kiss' is the wordplay.
'upset' is an anagram indicator.
'about' indicates putting letters inside.
'a kiss' becomes 'x' (X can represent a kiss).
'one' anagrammed gives 'oen'.
'oen' enclosing 'x' is 'OXEN'.
'getting' is the link.
(Other definitions for oxen that I've seen before include "Bovine animals, in yoke" , "Domesticated bovine draft animals" , "Steers" , "Draught animals" , "Cows and bulls" .)