Hoppers contain the paintball supply for a marker, much as magazines contain the ammunition on a regular rifle.
With few exceptions, hoppers are all mounted above the marker, and most use gravity as the ultimate force to get the balls in the marker.
That is to say, if most hoppers are turned upside down, the marker will not be fed with balls and will cease to fire.
45 Ball Hopper
GXG 200 Round Hopper.