He goes inside to backed-up loo where one may get the runs (3,4)
I believe the answer is:
the oval
'where one may get the runs' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'he goes inside to backed-up loo' is the wordplay.
'he goes' becomes 'the' (I can't justify this - if you can you should give a lot more credence to this answer).
'inside' says to take the centre.
'to' becomes 'for'.
'backed up' shows that the letters should be reversed in order.
'loo' becomes 'lav' (lavatory).
The central letter of 'for' is 'o'.
'lav' written backwards gives 'val'.
'the'+'o'+'val'='THE OVAL'
Can you help me to learn more?
(Another definition for the oval that I've seen is " London cricket ground".)