Row about a custom (4)
I believe the answer is:
tier
'row' is the definition.
(a tier is a row of things)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for tier that I've seen before include "Rite (anag.)" , "Storey" , "Level within hierarchy" , "Row, level" , "He might do sailor's knots" .)