The most common and most likely answer to this crossword clue is the 5 letter word DRANK
I've seen this crossword clue in The Times
D
R
A
N
K
More clues leading to the result DRANK
- Daughter, standing, gets knocked back
- Took on water maybe — unpleasantly wet crossing river
- Condition after last of bread; toasted maybe?
- Drained delta on estate
- Duke superior to soldiers perhaps took a shot
- Duke superior to soldiers took a shot perhaps?
- Row after daughter had a Guinness, say
- Consumed by row with Democrat
- Director, foul, had G&T maybe
Buddy explains!

The straight part
We know that "knocked back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knocked back = drank.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DRANK mean?
DRANK noun- Dextromethorphan
- A drink, usually alcoholic
- To consume (a liquid) through the mouth.
- (metonymic) To consume the liquid contained within (a bottle, glass, etc.).
- To consume alcoholic beverages.
- To take in (a liquid), in any manner; to suck up; to absorb; to imbibe.
- To take in; to receive within one, through the senses; to inhale; to hear; to see.
- To smoke, as tobacco.
- Wild oats, or darnel grass.