This photo is from version 1, I'll be making a second version because i accidentally ripped a piece of the cloth and had to rip it all.
So, let's start!
Step 1: What Do I Need?
Step 2: Begin Cutting
Note: in some tennis balls (mostly with black interior), the cloth is not connected to the rubber with strings, here you can make a vertical cut first, and then follow the seam. Skip the next steps then.
Photo 1: middle between two lines
Photo 2: Cut
Step 3: Keep Cutting
Note: If it is too difficult to keep the fabric on, you can also rip it totally out, like in my version 1.
Photo 1: Parallel with the lines
Step 4: JUNCTION!
Step 5: Finished!
You can also combine, put them upside down, or even use 2 full tennis balls without any cutting.