This Instructable describes a very simple idea, and I'm sure you could figure it out how to make a pair of your own sneaker balls without reading, but what the hey... here it is anyway!
Step 1: Acquire Materials
You'll only need a couple things to make a pair of the deodorizers:
1) two plastic containers from the inside of a Kinder Surprise Egg (or whatever else you have lying around that you can poke holes in, fits in your shoes, and can open/close)
2) a couple spoonfuls of baking soda
3) two tea bags
4) two small safety pins (or staples)
5) a thumb tack
Right... onto the construction!
Step 2: Fill the Tea Bags
The tea bags are a convenient way of housing the baking soda without having it leak all over the place. Take your tea bag and open it up. I used a round one, so I cut a small hole in mine. Otherwise, just take out the staple. Remove the loose leaves. You might as well get some hot water going and steep them while you complete the remaining steps.
If you need, grab a funnel and fill up the now empty bag with baking soda. The baking soda is the active ingredient and soaks up the nasty odours from your shoes. You can also add other scents by adding them with the baking soda. I just went went with baking soda because my philosophy is that the only thing worse than the smell of sweat in a locker room is the noxious mixture of Axe AND the smell of sweat in a locker room :P Same goes for my shoes.
When you're all done filling it, you need to close the bag back up. I used a small safety pin to close it , but you could just staple it back together.
Step 3: Make Holes!
Grab your thumb tack and Kinder Surprise container and start making holes so air can get in and out. I only poked a couple because my hand started hurting, although you could probably poke some really neat patterns or decorate it however you like.
And of course, be careful to not poke yourself.
Step 4: Assemble
Now just put it all together. Stick the baking soda tea bag into the container, close it up, place one in each shoe, and enjoy your now less stinky shoes!
You'll have to change the baking soda every so often to maintain the freshness, but that shouldn't be a problem because you can just pop open the Kinder Surprise containers and change out the tea bag.