Goosechase Stadium is a minigame map that supports two custom gametypes: Ballchase and Gluttonous Geese. The map itself is a giant bowl-shaped stadium, completely enclosed and specially designed for these frenetic, fast-moving games. As for the games:

Ballchase is a variation on rocket race. The core mechanics are the same - you and your partner drive a mongoose around, with the passenger blasting away (in this case with a concussion rifle, not a rocket launcher). And you're trying to win a rally by getting to 15 flag points. In this case, the flags are actually golf balls which are rolling and flying around. This game's recommended size is 3-5 teams of 2 players each. You can play up to 8 teams, but that will probably be a little too chaotic - I've found 4 teams to be about the sweet spot.

Gluttonous Geese is based on Haloball and pretty much just converts mongooses into goals. Drive one of your team's mongooses into a golf ball to score a point. Unfortunately there are some minor, uncontrollable quirks with this - I can't prevent people from stealing the other team's vehicles (not that that does you any good) or just running around on foot (though there are soft kill zones that only affect pedestrians through most of the stadium). Your best bet for winning is to make sure you stay on a mongoose that has a waypoint above it - those are your own team's goals. The game is also divided into 4 short rounds of 2 minutes each, so things should never get too crazy before a new round resets everything. One quirk which is more amusing than problematic - the constant barrage of sound effects from scoring seems to break the announcer's brain. My friends got a lot of laughs out of the announcer shouting "ACTION SACK!" and "10 SECONDS REMAINING!" at random times in the middle of rounds.

DOWNLOAD THE GAMETYPES HERE: Ballchase | Gluttonous Geese

Video

YouTube - Goosechase Stadium (Halo: Reach map)

Screenshots (note: screenshots were all taken in a beta version of the stadium - the only visible change is in the four bases in each corner, which are now inclined to prevent balls from just sitting there)