Motorcyclist repressing constant row (6)
I believe the answer is:
bicker
'row' is the definition.
(bicker is a kind of row)
'motorcyclist repressing constant' is the wordplay.
'motorcyclist' becomes 'biker' (I've seen this before).
'repressing' means one lot of letters goes inside another.
'constant' becomes 'c' (mathematical abbreviation).
'biker' placed around 'c' is 'BICKER'.
(Other definitions for bicker that I've seen before include "Clash" , "Argue over petty things" , "Quarrel feebly" , "Quarrel over petty things" , "Quarrel about unimportant things" .)