The most common and most likely answer to this crossword clue is the 4 letter word BALL
I've seen this crossword clue in Financial Times
B
A
L
L
More clues leading to the result BALL
- Delivery of inflatable bags, half going astray
- Regularly fall ill after bachelor party
- Event giving rise to Liberal party
- Dance nut
- Party nut
- Bouncer for the dance
- Left party upset, but another one’s found
- Left backing return of Labour Party
- Leaving Oxford college, I look back
- Party in retreat — Liberal Party (4
Buddy explains!

The straight part
We know that "co-operate to play this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case co-operate to play this = ball.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 BALL mean?
BALL noun- A solid or hollow sphere, or roughly spherical mass.
- A round or ellipsoidal object.
- (mildly, usually in the plural) A testicle.
- A leather-covered cushion, fastened to a handle called a ballstock; formerly used by printers for inking the form, then superseded by the roller.
- A large pill, a form in which medicine was given to horses; a bolus.
- To form or wind into a ball.
- To heat in a furnace and form into balls for rolling.
- To have sexual intercourse with.
- To gather balls which cling to the feet, as of damp snow or clay; to gather into balls.
- (usually in present participle) To be hip or cool.
- To play basketball.
- To punish by affixing a ball and chain
- An appeal by the crowd for holding the ball against a tackled player. This is heard almost any time an opposition player is tackled, without regard to whether the rules about "prior opportunity" to dispose of the ball are fulfilled.
- A formal dance.
- A very enjoyable time.