it's possible to have baseball sized hail.
due to climate change it's happened more often recently. to put it into perspective I have see baseball sized hail five times in my life. four of those have been in the last five years.
I'm not driving in baseball sized hail. in my book that IS an emergency.
for the Euroly-challenged, that's a hailstone thats around 7-7.5 cm in diameter. I've driven through 2cm hail before, not fun but just go slow. anything less than that doesn't really need you to pull over IMO.