The most common and most likely answer to this crossword clue is the 4 letter word BLAG
B
L
A
G
More clues leading to the result BLAG
Buddy explains!

The straight part
We know that "Robbery" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case robbery = blag.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 BLAG mean?
BLAG noun- A means of obtaining something by trick or deception.
- An armed robbery.
- To obtain (something) for free, particularly by guile or persuasion.
- (specifically) To obtain confidential information by impersonation or other deception.
- To pick up someone.
- (1960s) To inveigle by persuasion.
- (1940s) To deceive; to perpetrate a hoax on.
- Fake, not genuine.
- An onomatopoeia for the sound of a falling strike.