Part of fence catching small rider in Grand National lottery? (10)
I believe the answer is:
sweepstake
'grand national lottery?' is the definition.
'sweepstake' can be an answer for 'lottery?' (sweepstake is a kind of lottery). I am not certain of the 'grand national' bit.
'part of fence catching small rider' is the wordplay.
'part of' is an insertion indicator.
'fence catching' becomes 'stake' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'small' becomes 'wee' (Scottish term for small).
'rider' becomes 'PS' (a rider is a clause added to a contract, so a P.S.).
'wee'+'ps'='weeps'
'stake' enclosing 'weeps' is 'SWEEPSTAKE'.
'in' is the link.
Can you help me to learn more?
(Other definitions for sweepstake that I've seen before include "lots here" , "gamble" , "prize" , "action on race" , "I'd bet on it" .)