It had grown more and more dangerous, also; for, by dint of playing it, Billy, who had started as a fat, clumsy, and sulky beast, had grown thin, nimble, and vicious.

Alloway, indeed, often declared that he did not know what ailed the ram; his food never seemed to be doing him any good, and neither man, woman, nor child dare cross the field in which he browsed.
The game lasted some twenty minutes; and Tinker's skill, sureness, and lightness of movement was the prettiest sight.

Sometimes, with a snorting bleat, Billy would turn sharply at the end of his charge, and charge again; then the concentration on the matter in hand, which his father had so carefully cultivated in Tinker, proved a most fortunate possession: he was never caught off his guard.

But he was beginning to think that he had had enough of it, and Billy was sure that he had, when there came a roar from the road, and there sat Alloway on his horse.

Or rather, he was no longer sitting on his horse, he was throwing himself off it.
Without one word of thanks to his playfellow for the pleasant game he had enjoyed with him, Tinker bolted for the further hedge, Billy after him, and Alloway after both.