three-legged race
A race in which two people run together with their adjacent legs tied together.
I participated in the three-legged race at the sports day.
close cooperation; working in tandem
Figurative use describing two parties (people, companies, etc.) working closely together toward a single goal, as if tied together like in a three-legged race.
The two companies developed the new product in close cooperation.
My husband and I have built up our little shop working closely side by side.
I ran a three-legged race with a friend at the sports day.
They got through the financial troubles by working together in tandem.