The most common and most likely answer to this crossword clue is the 7 letter word GYMNAST
I've seen this crossword clue in The Guardian
G
Y
M
N
A
S
T
More clues leading to the result GYMNAST
- Angst aroused about Cyclops’s upset tumbler?
- Flexible performer gave voice about my flips and tumbles, primarily
- Tangy M&S shakes in tumbler?
- He may resort to clubs and bars, but should be fit
- Many G and Ts poured out in tumbler
- Flying gnats surround head of young male athlete
- Girl madly nasty about man athlete
- Athlete gets indirect tax cover for many sports
- GST has confused many — one has to twist, turn and somersault to get through
- My stag involved necking last of poteen tumbler
Buddy explains!

The straight part
We know that "Flexible performer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flexible performer = gymnast.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 GYMNAST mean?
GYMNAST noun- One who performs gymnastics