I'm no expert. From watching the film, it looks like it works like this:
Tom Cruise (the Stranger) goes into a pool hall and starts playing for money. He plays very well. He never misses a shot. He basically cleans the room.
After a while, Paul Newman and the Girl (2 Brothers), come into the pool hall and start drinking and watching the game. They're obnoxious and make rude comments.
Now, a difficult shot comes up.
Spectators in the pool hall that have seen how good Tom Cruise is, have no doubt that he can make it. Paul Newman says, "No way...he'll choke...blah blah."
Paul Newman offers to bet that Tom Cruise will miss. Spectators make the bet ($1000). Tom Cruise misses on purpose. Paul Newman gets paid.
They all leave separately. Only they know they've been working together.