With winter here, lag (4,6)

I believe the answer is:

fall behind

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

'lag' is the definition.
(I know that lag can be written as fall behind)

I don't understand how the rest of the clue works.

(Another definition for fall behind that I've seen is " Lag".)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app