Need a little help with Forge.

So, recently I've started building a race track on forge and its looking pretty good so far. But I have this inclined road on the map that I'd like to roll soccer balls down but Forge wont allow me to because once I spawn it in Forge, it rolls, falls of the map (as it should), and never respawns. I've tweaked the settings so it spawns after one second but the problem still remains. How do i fix this?