The good news is a rubber ball really can't damage them.
The bad news is something is wrong and touchy feely isn't going to fix it. Resign yourself to the fact that the socks have to come off, and that means the side trim has to come off, and just do it as carefully as you can.
If your speakers are so old they needed to be sent to the factory the odds are the other poster was correct and that one of your bracing bars has come undone. Magnepan wouldn't have done anything about this and I find when the wires start to go, these things do as well.
Obviously you'll want to check the driver side out as well, but it's likely a bar is your problem. If the ball however popped a mid panel wire, simply DAP it back down.
If it is a bar, check the rest of them while the sock is off. If you can pry them off even a little pull them off all the way and re-epoxy them back on now. You don't want to fix this, resock it, and have it happen again to another bar in 3 months. Note that they are supposed to have a bend in them, so don't lie the driver flat while the epoxy cures. Leave it stand propped upright so the bend can happen.
Good luck with the repair, and I'd have a talk with the other half about throwing things at your speakers in future. :^ )
It's all about the music...