In pain, perhaps, increased one's bet (7,2)
I believe the answer is:
doubled up
'in' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs sometimes mean the same thing.
'pain perhaps increased one's bet' is the wordplay.
I cannot really understand how this works, but
'increased' could be 'up' (something that's up has increased or risen) and 'up' is present in the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for doubled up that I've seen is " Bent in two".)