I don't recall the name, but I have fond memories of a Arthur C. Clarke story about a football game set in a nameless South American country where the ref is grossly biased. One wealthy sponsor pays for about a hundred thousand souvenir programmes that are essentially a couple of square feet each of reflective metal, and on a prearranged signal the supporters of the losing team all reflect sunlight at the ref at once... it's never quite established whether the culprit intended to reduce the ref to a small pile of ashes, or just hadn't checked the numbers beforehand.

(It occurs to me in hindsight that aiming gets harder as the number of people involved increases, so it probably wouldn't be quite as devastating as that, but it was a cute story.)