The goals in Grifball are Hill Markers (the Capture Plates are inactive) to keep the goal waypoint out of your FoV. Halo 4 Hill Markers have an animation like they are burning up in a small column of fire when they move or deactivate. Standing within this effect can strip away half of your shields.
There is a mini game in my file share called
Throwin' Stones, played on a map called
Glass House. It's an Action Sack style KotH game where you take turns throwing stones (Rockets) at each other. If you stand under the Hill Marker when the hills switch sides your shields will be stripped and you will feel a small explosion like you would in Grifball.