Runs? Yes, ten! (3)
I believe the answer is:
six
'runs? yes' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'ten' is the wordplay.
I cannot really understand how this works, but
'ten' could be 'x' (Roman numeral) and 'x' is present in the answer.
The remaining letters 'si' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for six that I've seen before include "larger boundary" , "Knock for . . . - surprise or defeat" , "Number of bowls in a cricket over" , "Half a dozen" , "Maximum cricket hit" .)