For a sportsperson it would have been more hazardous to have run one at the start (5)
I believe the answer is:
skier
'for a sportsperson it would have been more hazardous to' is the definition.
I can't judge whether this definition defines the answer.
'run one at the start' is the wordplay.
'run' becomes 'ski' (I've seen this before).
'one at the start' becomes 'er' (I can't explain this - if you can you should give a lot more credence to this answer).
'ski'+'er'='SKIER'
'have' is the link.
Can you help me to learn more?
(Other definitions for skier that I've seen before include "Winter sportsperson" , "He glides across snow for fun" , "Winter sports person" , "He glides over snow, perhaps in sport" , "Winter sportsman" .)