An early one doesn't get trodden on! (5)
I believe the answer is:
riser
'an early one' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for riser that I've seen before include "found on the staircase" , "Upright piece between steps" , "person advancing position?" , "A bit of a flight" , "Vertical piece between two steps of stairs" .)