Cricketer without runs a rude youngster (4)
I believe the answer is:
brat
'a rude youngster' is the definition.
'brat' can be an answer for 'youngster' (brat is a kind of youngster). I'm unsure of the 'a rude' bit.
'cricketer without runs' is the wordplay.
'cricketer' becomes 'bat' (I've seen this before).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'runs' becomes 'r' (cricket abbreviation).
'bat' enclosing 'r' is 'BRAT'.
Can you help me to learn more?
(Other definitions for brat that I've seen before include "Ill-mannered child" , "Brash young type" , "annoying young fellow" , "Nasty child" , "An obnoxious or spoiled child" .)