So, I broke my 6 iron on the range the other day after hitting around 10 balls in a row with it. Anyone else snapped a shaft in the same place as this?!
I was annoyed when the shaft hit me round the back of the neck, but almost started to laugh when I saw how it broke. But as you say, an S300 shaft is relatively cheap.
Have you thought about loosening your grip a little.
I would say that at some time you've tweaked it getting it out of the bag or walking through a door to the range as there has to have been some sort of damage to the shaft for it to fail there.