The most common and most likely answer to this crossword clue is the 4 letter word STUN
I've seen this crossword clue in The Times
S
T
U
N
More clues leading to the result STUN
- Crazy to turn up and cause sensation
- Turning heads in surprise
- Stagger round the bend in retreat
- Recurved bananas make quite an impact
- Get amazed with temperature in star
- Bowl over, with very hot ball trapping opener in test
- Crazy upset brings shock
- Teachers' union's reeling in shock
- Shock as spectacular feat is left unfinished
- Shock upset when golf is cancelled
Buddy explains!

The straight part
We know that "Shock" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shock = stun.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 STUN mean?
STUN noun- The condition of being stunned.
- That which stuns; a shock; a stupefying blow.
- A person who lacks intelligence.
- The effect on the cue ball where the ball is hit without topspin, backspin or sidespin.
- To incapacitate; especially by inducing disorientation or unconsciousness.
- To shock or surprise.
- To hit the cue ball so that it slides without topspin or backspin (and with or without sidespin) and continues at a natural angle after contact with the object ball