The most common and most likely answer to this crossword clue is the 9 letter word STITCHING
I've seen this crossword clue in The Guardian
S
T
I
T
C
H
I
N
G
Buddy explains!
The straight part
We know that "theatrical closure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case theatrical closure = stitching.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 STITCHING mean?
STITCHING verb- To form stitches in; especially, to sew in such a manner as to show on the surface a continuous line of stitches.
- To sew, or unite or attach by stitches.
- To practice/practise stitching or needlework.
- To form land into ridges.
- To weld together through a series of connecting or overlapping spot welds.
- (graphics) To combine two or more photographs of the same scene into a single image.
- (more generally) To include, combine, or unite into a single whole.
- Stitches, collectively.