Now he only saw her as someone to be defended, someone who was his, someone even who depended on him for support.

He would have challenged a whole world of Deans in her defence.
He said something, but no one could hear his words; then he sprang upon the startled Ernest.
It was not a very distinguished combat; it was Jeremy's first battle, and he knew at that time nothing of the science of fighting.

The Dean's Ernest, in spite of his term at school, also knew nothing--and the Dean's Ernest was a coward...
It lasted but a short while, for Mary, after the first pause of horrified amazement (aware only that Ernest was twice as big as her Jeremy), ran to appeal to authority.

Jeremy himself was aware neither of time nor prudence.

He realised immediately that Ernest was a coward, and this realisation filled him with joy and happiness.