The most common and most likely answer to this crossword clue is the 10 letter word HIPPODROME
I've seen this crossword clue in The Guardian
H
I
P
P
O
D
R
O
M
E
Buddy explains!

The straight part
We know that "theatre" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case theatre = hippodrome.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 HIPPODROME mean?
HIPPODROME noun- A horse racing course.
- A fraudulent sporting contest with a predetermined winner.
- A circus with equestrian performances.
- To stage a sporting contest to suit gamblers.