One raising boundary marker for sportsman (6)
I believe the answer is:
fencer
'for sportsman' is the definition.
(I've seen this before)
'one raising boundary marker' is the wordplay.
I cannot quite see how this works, but
'boundary marker' could be 'fence' (I've seen this in another clue) and 'fence' is found within the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fencer that I've seen before include "One using foil, epee" , "who may intervene to keep neighbours apart?" , "One skilled with a sword" , "A sword sportsman" , "armed man" .)