In pairs, back to back, knees bent, no balls. Each player gets low and tries to push the other back.
Variation - pairs are in the free-throw and centre circles, each player trying to get the other out.
Bob Hurley - Bob Huggins "Gentle Ben" - each pair of players begins by sitting down with their backs against each other, on coach's whistle they spring up, push against each other using their backs (elbows out, hands up), hold a box-out for 2 seconds (or 5 seconds) then leap in the air to snatch an invisible rebound with both hands.
Jay Triano - four players, two players are low, back-to-back, each has a ball and passes with the player they are facing.