some use a plastic injection mould, this method costs a lot of money as the tooling alone will set you back 10k easily. the older method is making it in two parts stitching the pattern together turning it inside out and using a valve system to seal it and for filling ball with air as was done by the old leather footballs of the 60s to 80s, this is quite hard as the stitching needs to be tight and the valve system needs to be able to seal totally.
