Crossword Genius

When beer starts to run over, be attentive (5)

Ross

I believe the answer is:

alert

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

'attentive' is the definition.
(I've seen this in another clue)

'when beer starts to run over' is the wordplay.
'when' becomes 't' (I can't justify this - if you can you should believe this answer much more).
'beer' becomes 'ale' (type of beer).
'starts to' indicates taking the first letters.
'over' is a charade indicator (letters next to each other).
The initial letter of 'run' is 'r'.
'ale'+'r'='aler'
't' after 'aler' is 'ALERT'.

'be' acts as a link.

Can you help me to learn more?

(Other definitions for alert that I've seen before include "Watchful and observant" , "In state of watchfulness" , "Signal danger" , "Watchful, sharp" , "Danger warning" .)

I've seen this clue in the Sydney Morning Herald.
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