I simply added the soccerball to Terminal (triplicate.map), gave it the phmo of the assault bomb and the effe of the active camo, and had the plasma grenade's explosion spawn the soccerball bloc. The spawned bloc lasts a short time and eventually disappears.
all the map changes:
1. Plasma Grenade - Plasma Shield
2. rocket spawns explosives and a wraith blast (What? It's fun.)
3. battle rifle is single shot (more like the E3 demo)
4. if it counts, I changed the lightmap slightly
yet to be done:
1. the visual effect for the inside of the bubble
2. the assault bomb or whatever else generating the bubble
3. the generator able to be destroyed, resulting in the shield deactivating
There are screenshots, yes:

I enjoy watching the projectiles stop in mid air.

I can spawn as many plasma shields as I can throw.

Very similar to the very ineffective bubble shield effe on a previous mod. I used Working Halo 3 Bubble Shield (not really 'working') as a base by accident, so the magnum may still spawn something. Easily fixed in dotHalo or Insolence.
Download: http://www.fantasyjam.net/h2files/ppf/bubbleshield.sppf
I may include a video recording later.
Be sure to post your opinion of my mod. It's my first one, and I'm really proud of it, so say it's awesome.