Row concerning whose turn it is to catch up (4)
I believe the answer is:
tier
'row' is the definition.
(tier is a kind of row)
'concerning whose turn it is to catch up' is the wordplay.
'concerning' becomes 're'.
'whose turn it is to catch' becomes 'it' (as in the playground game 'it').
'up' is a reversal indicator (in down clue: letters go upwards).
're'+'it'='reit'
'reit' reversed gives 'TIER'.
(Other definitions for tier that I've seen before include "Level - layer" , "Level within hierarchy" , "'Level, grade (4)'" , "I might draw" , "Row, layer" .)