Knock back lager and fall over (4)
I believe the answer is:
slip
'fall over' is the definition.
'slip' can be an answer for 'fall' (I've seen this in another clue). I am unsure of the 'over' bit.
'knock back lager' is the wordplay.
'knock back' is a reversal indicator.
'lager' becomes 'pils' (Pilsner beer).
'pils' back-to-front is 'SLIP'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for slip that I've seen before include "Loose one's footing" , "release > voucher" , "Lingerie item - fielding position" , "Silly little mistake" , "printer's proof" .)