Crossword Genius

Attack unexpectedly, once up and running (6,2)

Ross

I believe the answer is:

pounce on

I'm a little stuck... Click here to teach me more about this clue!

'attack' is the definition.
I know nothing about this answer so I can't judge whether this works.

'unexpectedly once up and running' is the wordplay.
'unexpectedly' indicates an anagram.
'and' is a charade indicator (letters next to each other).
'running' becomes 'on' (eg when a machine is running it is on).
'once'+'up'='onceup'
'onceup' is an anagram of 'pounce'.
'pounce'+'on'='POUNCE ON'

Can you help me to learn more?

I've seen this clue in The Independent.
Want a hint initially instead of a full solution? Install my app