Barry,
Your stoma should NEVER get anywhere near the size you're describing, unless a baseball by you is smaller than a ping-pong ball here in the States. Whoever told you that is a moron. Sorry to be so blunt. FIND ANOTHER DOCTOR AND DO IT FAST!
If any part of your intestine swelled to the size of a baseball, there would be cause for alarm. Your colon has a thicker wall than your small bowel, since it works as a trash compactor of sorts, but it's your sphincter muscle that keeps everything from escaping out your butt. With an ostomy, that muscle is no longer in play, so there's nothing to stop the flow and allow it to 'compact', if you will. So your output should flow out into your bag pretty much unimpeded and not get all bunched up to form something the size you describe.
You have me curious now... what exactly happens after your stoma swells to that size? Does everything come rushing out like an explosion, or is your output solid and firm? I can't imagine living with what you are describing! I think the expression is OMG! Take a pic and show BOTH your GASTRO and your SURGEON... but be prepared to find better docs if either says it's normal! Keep us abreast of what happens.
;O)