Soccer ball

The Soccer Ball is an easter egg found in the Halo 2 Campaign level Metropolis, hidden in the rooftops. There is speculation that it was used by Bungie to test the physics engine of the game, and that they left it in the level instead of deleting it.

A red ball similar to the Soccer Ball is shown in the Limited Edition DVD. There is a section that talks about the special testing level that Bungie uses to test weapons, enemies, vehicles, environmental effects, sounds, and other game mechanics. One of the scenes portrays a Warthog driving and moving the ball around.

First Method
To get to the Soccer Ball, retrieve the Scarab Gun and get back into the Banshee. Then head along the highway after the amphitheater until you find a building with a huge chunk taken out of it. At the bottom of the hole you will see the giant Soccer Ball. If you manage to get it out before the Scarab comes by, you can watch the Scarab kick the Ball around on its way to the canal. The Scarab Gun is also good for pushing the Soccer Ball around.

Second Method
There is actually another uncommon way to get to the Soccer Ball. If you are not able to get the Banshee to that part of the map, don't fret. All you need is to play the level in co-op and have a Wraith.

Position one person (Person A) at a certain position below a smaller building that is also missing a chunk -- you will see the building as soon as you walk back out in to the street. Have the second person (Person B) drive the Wraith. Both people should face each other. Person B should boost with the Wraith, and Person A should jump. If Person A times the jump properly, they will be boosted onto the broken part of the building. At this point, Person A should look around; they will see two metal things sticking out, one on each side. They should jump onto the lowest of the two, jumping from there onto the second. Here, Person A should jump up and on top of the building, proceeding to walk around until they see a raised area with a fence-type thing on it. It is missing a part on the wall, so Person A should jump up and through the hole, and walk up to the building mentioned in the first method; from there, they can walk directly to the Soccer Ball. They can melee it and move it until they knock it off the building and onto the ground.

Person A should get themselves down and into a second Wraith, allowing them and Person B to play soccer with the Ball.... and Wraiths.

Third Method
If you know where the Ball is located and just don't know how to get up there, follow these steps. When you come to the part when you can assassinate the Jackal and steal his Beam Rifle, look for the Gauss Warthog and go through that area. In the next part, stay in the 'Hog until you're able to kill everything, but leave one Ghost. Get in the Ghost and ride up to the part where you recon with the Marines (and eventually jump onto the Scarab). Make sure you jump onto the Wraith and beat down the driver. Get into the Wraith and drive to the area with the Ball. Fire plasma mortars into the area; after a while, you should eventually be able to blast the Soccer Ball down to the ground.

''This may require the Sputnik Skull. It would be wise to try the other methods first.''

Fourth Method
For this method, the Sputnik Skull is highly recommended. In Metropolis, after the waterfall part (the entrance is guarded by a Wraith and two Jackal Snipers) there is a big building with a large piece of broken glass in front of the entrance you just exited. Jump onto the ledge and grenade jump into the big glass crack. From there, navigate up the support beams. This may take a few tries, as you need to run and jump from the right spot. No grenade jumps are needed here. Once on the top support beam, you can exit the roof. From there get to the Ball; it's around the corner with the trees. Melee it off the building if you please (Sputnik is making this relatively easy). If you jump off, you'll die, so you instead need to backtrack down into the room with the debris, jump down the the small ledge, and onto the ground. From there you (and your partner, if present) can board a Wraith and use its boost to play soccer. This is guaranteed to work, but may prevent you from getting the Scarab Gun.

Fifth Method
Also, you can get the Sputnik Skull, and then go to Metropolis. At the point where you come past the area with the waterfall, you will see a ledge covered with trees up high, next to the Soccer Ball. Get a Warthog, and make sure it has three people in it (including you), otherwise it won't work. Face directly in front of the ledge, on the raised part in the middle of the road. Now throw a grenade at the back wheel, and hop back in. With luck, the Warthog will flip through the air onto the ledge of the half broken building. If it doesn't get into the building, just grenade jump up.

Sixth Method
Play until you can get into the Gauss Warthog. Get in, kill everything and then, past the waterfall, in the second city part, you will see a broken window. With the Sputnik Skull on, take a Rocket Launcher and go to the ledge under the broken window. Stand on the edge, and shoot at the ground in front of you as you jump. Be sure to hold back on the left thumbstick. When you land, wait to recharge your shields. Jump onto the lowest steel beam. Line yourself up, and rocket jump like you did before. You will land either really close to or on the top. Once on top, go and jump across the gap. The Soccer Ball is in the shadows. Use grenades to get it down onto the streets. WARNING: Rocket jumps are more dangerous, but more accurate than grenade jumps.

Playing Soccer
Once you get the soccer ball, the bridge you have to cross at the beginning of the level is perfect for playing soccer if you're in co-op. If you have two ghosts, then you can use the entrance to the tunnel as one goal, and the starting point of the level as the other. If you use a wraith or a banshee, it will probably make the ball fly into the water, so just stick with ghosts. This will work the best if you used the Sputnik skull to get the ball.

Soccer Ball in Halo 3
While not an Easter egg, the Soccer Ball appears on the levels, Foundry, Standoff, Rat's Nest, Avalanche, Ghost Town, Cold Storage, Assembly, Orbital and Blackout as a Forge object. It appears to be smaller than the ball in Halo 2, although the physics are much more accurate for it. The Gravity Hammer is often used to play soccer, but the Soccer Ball also responds to the Rocket Launcher, Scorpion and Wraith shots, and melees. Melees are the most effective way of controlling the Ball, as it will not reach velocities much higher than those of the player. The Soccer Ball, when at a high enough velocity, can kill normal players. It is often fun to see a contraption launch a soccer ball at somebody. The Soccer Ball can be manipulated by the right bumper, akin to vehicle flipping, as well.

Trivia

 * The Halo 2 Soccer Ball is larger than the Halo 3 one.
 * The Soccer Ball was most likely created by Bungie for testing. It was either forgotten, or Bungie may have left it there as an Easter egg.