Father goes after son, having tense disagreement (4)
I believe the answer is:
spat
'disagreement' is the definition.
(spat is a kind of disagreement)
'father goes after son having tense' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'goes after' means one lot of letters go next to another.
'son' becomes 's'.
'having' says to put letters next to each other.
'tense' becomes 't' (abbreviation used in many dictionaries).
'pa' after 's' is 'spa'.
'spa'+'t'='SPAT'
(Other definitions for spat that I've seen before include "Small quarrel between Pats" , "Small altercations between Pats" , "Petty quarrel or fight" , "Ejected saliva from the mouth" , "Expelled" .)