Instructions
Have the other player press and hold the "B" button on the Xbox 360 ("O" button on the PS3) to make his character lie down.
Push the left thumbstick on your controller all the way forward to make your character walk. Walk as far away from the other player as you can and then turn around to face him.
Start walking toward the other player. Click the left thumbstick down while your character is walking to make your character run.
Press and hold the "B" button ("O" button on the PS3) as soon as you get close to the player to dive on top of him. Note that you must still be running in order for this command work.