|Stuffing shirts is less awkward|
when it is your own shirt
So this activity encourages getting the ball over the net and sending it to a target. Variation: have teams serving cross-court to their Stuffer.
In the original game the Stuffer was stuffing a t-shirt or jacket, presumably worn by another team member. By changing this to a hopper we have no one standing around getting stuffed <g> and no awkwardness about stuffing someone else's clothing with tennis balls.
*Having difficulty selecting a Stuffer? Try Fing Fong Fooey.