Rings bookie up. That's torn it! (4)
I believe the answer is:
oops
'torn it' is the definition.
I can't tell whether this defines the answer.
'rings bookie up' is the wordplay.
'rings' becomes 'oo' (multiple circles).
'bookie up' becomes 'ps' (I can't explain this - if you can you should believe this answer much more).
'oo'+'ps'='OOPS'
'that's' is the link.
Can you help me to learn more?
(Other definitions for oops that I've seen before include "Exclamation on making a minor mistake" , "statement after accident" , "Clumsy me!" , "Blunder explanation" , "I've made a mistake!" .)