Green thumb

Green Thumb is a controller setting for Halo: Combat Evolved, Halo 2, and Halo 3. It involves switching the B button and the right thumb stick click from default. This makes the B button zoom and a Right thumb stick for melee.

Button Layout
Y button: Swap weapons.

X button: Use equipment.

A button: Jump.

B button: Zoom view.

Left trigger: Shoot left weapon/throw grenade.

Right trigger: Shoot right weapon.

Right thumbstick: melee.

Left thumbstick: Crouch.

"Green Thumb" is the best layout for players that melee on a constant basis. With this, players face disadvantages with Snipers and other Scoped weapons, but it provides instant access to a melee attack at close range, which serves great chances at winning a close-quarters battle.

Trivia

 * Green Thumb often helps Call of Duty players play Halo, due to the similar controls.