The most common and most likely answer to this crossword clue is the 7 letter word SHOCKER
I've seen this crossword clue in The Times
S
H
O
C
K
E
R
Buddy explains!
The straight part
We know that "Terrible performance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case terrible performance = shocker.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 SHOCKER mean?
SHOCKER noun- One who or that which shocks or startles.
- A device for giving electric shocks.
- A particular hand gesture with a sexual connotation.
- Sexual act related to the shocker hand gesture: two in the pink, one in the stink.