Serious point about runner's odds (7)
I believe the answer is:
earnest
'serious' is the definition.
(similar in meaning)
'point about runner's odds' is the wordplay.
'point' becomes 'NE' (NE is an example).
'about' means one lot of letters goes inside another.
'runner's odds' becomes 'earst' (I can't explain this - if you can you should give a lot more credence to this answer).
'ne' put within 'earst' is 'EARNEST'.
Can you help me to learn more?
(Other definitions for earnest that I've seen before include "Sincere -- humourless" , "Resolute" , "Fixed" , "Art worthy" , "Pledge - far from frivolous" .)