The
Fine Art of Grenade bowling.
Grenade bowling is when you get a bunch of the other team up on the top of a ramp in some map. Then you proceed to "bowl" grenades at them. You get two shots, and points are how many people you kill. Bonus points if they disintegrate. If you intend to restack the remaining opponents having a medic on hand is ideal, so they aren't being bowled at with like 1 health, 0 armor.
I first saw this in Half-Life: TFC on the map shutdown. This one has a long ramp up to the capture point which is nice and straight.
Note: You cannot use special grenades, like Mirv's or the soldiers nail grenade. I imagine you could use concussion grenades, but it would be rather pointless.