Many years ago I used to have an instructor that was very liberal with the use of the fuel-stick across the knuckles in acknowledgement of any errors on my behalf -usually failing to deselect carb air on short finals... it wasn't unusual to come away from a 30 minute lesson with swollen, painful knuckles on the right hand.
Just read this entire thread from post #1. Must have missed it first time round as cannot remember it but was appalled at reading the quote above.
Any Instructor who would have taken such a liberty with me would only have ever done it once!
I would have left him in need of some medical care immediately after the landing, which would have been shortly after the 'incident' occurred.
In any case; Such behaviour is classed as 'assault.'
physicx; Take the matter to a higher authority, immediately!