what does the boy throw over jim and will?

I'm not sure exactly what part of the story you're referring to here, but I'll go with a section I remember. When the boys are fooling around in front of Mrs. Foley's house (fighting and such), someone who appears to be no more than a "boy" comes to stand on the porch.

But it isn't a boy, it's Mr. Cooger, and he throws handfuls of jewelry over, at, and next to the boys while yelling,"Help, police!" It's Mr. Coogar's plan to have them arrested for theft.