Green’s Dictionary of Slang

(US tramp) to throw a rock or stone.

1901		W.S. Walker In the Blood 158: ‘Dew-dropping,’ ‘dragging down’ or ‘flimpings’ more in our line.
1907		J. London Road 38: I know those shacks will fusillade me with rocks. A healthy shack can ‘dewdrop’ a pretty heavy chunk of stone on top of a car.
1927		‘Jargon of the Und.’ in DN V 444: Dew-drop, To heave lumps of coal in the air so as to fall at high angles upon the heads of hoboes riding between cars.
1931		Irwin Amer. Tramp and Und. Sl. 61: Dewdrop. – To hurl lumps of coal back over the train in hopes of striking a tramp riding between the cars.