Mark 9:20

‘And they brought him to him. And when he saw him immediately the spirit tore him grievously, and he fell on the ground and wallowed foaming.'

They went to fetch the boy who was being kept apart, probably under guard. And as soon as he saw Jesus (Luke brings out that it was while the boy was approaching), the effect of seeing Him was to disturb the dumb spirit which immediately expressed its dismay by an acute attack on the boy. But we note that it did not cry out, for it was a ‘dumb' spirit. Mere epilepsy alone would not have caused such an effect for naturally speaking there was nothing about Jesus which would produce an epileptic fit and the boy himself would not necessarily have known Jesus. And had it been only epilepsy Jesus would have dealt with it differently. Rather He was aware that there was a powerful spirit possessing the boy and that it was deeply disturbed. It had cause to be, for it knew that here was One Whom it could not resist or deceive.

As the boy approached Jesus it would appear that the crowd did not at first follow, leaving it to a few of their number to take the young man to Jesus.. They may well have been afraid to come too close to the situation until they were sure Jesus had it well under control. They were aware that what was being dealt with was very powerful. Or perhaps the disciples had asked them to give Jesus some room. But it seems that they watched at a distance to see what would happen. This gave Jesus space in which to ascertain the full situation.