Albert Barnes on Mark 9:18

And wheresoever. In whatever place, at home or abroad, alone or in public.

He teareth him. He rends, distracts, or throws into convulsions.

He foameth. At the mouth, like a mad animal. Among us, these would all be considered as marks of violent derangement or madness.

And pineth away. Becomes thin, haggard, and emaciated. This was the effect of the violence of his struggles, and perhaps of the want of food.

(1) "teareth" or, "dasheth" (c) "foameth" Jude 1:13