Someone might remember this from the old Toybox, yes I made that and I remade this one as well. This one is better suited for multiplayer, since it doesn't actually block the player physics , but it can still be kicked around. Press use on the ball to pick it up. The entity can be found under Spawnmenu > Entities > Fun + Games. This entity also works outside of sandbox, the classname is "sent_soccerball" if you want to spawn it in your gamemode.
Workshop http://steamcommunity.com/sharedfiles/filedetails/?id=293904092 Garrysmods.org https://garrysmods.org/download/8/soccer-ball