Crossword Genius

To be obliged to open sack was good (7)

Ross

I believe the answer is:

behaved

'was good' is the definition.
(to behave is to be good)

'to be obliged to open sack' is the wordplay.
'to be obliged' becomes 'have' (to be obliged is to have to do something).
'to open' indicates putting letters inside (some letters create an opening in a word).
'sack' becomes 'bed' ('in the sack' means 'in bed').
'have' inserted inside 'bed' is 'BEHAVED'.

(Another definition for behaved that I've seen is " Conducted oneself in a certain manner".)

I've seen this clue in The Guardian.
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