It’s hard to imagine the state of that headmaster’s mind, to even want to inflict such injuries, least of all carry them out.
I completely agree with the point I believe you were aiming to convey but I question what you have written. Where, at any point, do we know that the HM wanted to inflict such injuries?
You are correct in suggesting it is hard to imagine the state of the headmaster’s mind, but it is not uncommon for people under stress to become angry and do things that seem totally out of character. I think of road rage incidents as a regrettably common example – equally inexcusable and in some cases leading to injury or even death.
Anyone who is unable to control their anger is most certainly unsuitable for a career in the teaching profession – in any capacity.