Hard cane strokes that overlap can break the skin, it happened to me on one occasion. I don’t think it was deliberate and it was no big deal, just a few spots of blood, no more than you might get when pruning a rose bush and certainly less dangerous.
Justin, I sympathise with your animosity towards your headmaster, which presumably arose for other reasons you haven’t stated, but now you have got the matter off your chest I do think it’s time to let the matter rest. You can at least be safe in the knowledge that it wouldn’t happen today in the UK.