I KNOW these are TENNIS balls thus made to play TENNIS…BUT AS they do mention playing fetch with Fidelity, I feel I should COMMENT. My French bull dog/Boston Terror LOVES these BUT manages to STRIP the felt off in very short time leaving TWO non bouncing hemispheres that she kept cupping over her mushy face. That led to a bunch of INGROWN WHISKERS! OUCH! Plus it seems a bit of felt was EATEN based on yard clean up… THAT could have been disaster if too big a chunk eaten. Anyone want my 58 balls and hopper? 
Putting the hopper together was impossible. The molded plastic pieces are so warped that they could not fit together no matter what we did. Wanted this for playing fetch with the dogs. After the last review of the tennis balls I fear that this is complete junk…
I’m really sorry your hopper wouldn’t fit together. If you haven’t already, please use the Customer Service form to report the issue. They may be able to help with a solution.