Being invisible is useful for all kinds of things.  Henry also plays football in the school team:

Under the bridge, the air was dark and musty and stale.  He could see the other boys, late too, smoking a quick cigarette, a muddy football forgotten at their feet.  He shook his hair out like a dog and approached them.  Standing with his back against the rough wall, he nodded and one of the boys passed him the cigarette. Henry didn’t inhale, didn’t like smoking.  He did what the other boys did.  He played because they played.  He laughed when they laughed.  Smoked because they smoked.  That was part of remaining invisible.  He liked the passing of the cigarette from lips to lips like a secret.  He liked being there.  Being part of it.  Secretly.

But that was all it was. They were off again, out over the stile, through the hedge and there in front of him, across the road; the school gates.  Already the bus was waiting.  The other kids ignored him now.  He wasn’t part of it.  They tolerated him because of the football.  Apart from that he was almost invisible to them. That was part of the reason he was so good for the football team.  The opposing players were almost surprised to see him there in goal, as if they hadn’t noticed him until he made the save.  This made it very difficult for them to score at all, and Henry went weeks without letting in anything.  He was better off in goal.  From the goal he could watch them dribbling the ball, their rain-wet, white legs, bright in the momentary sunlight.  Henry didn’t like the challenges played out in open field.  He didn’t like to feel the hard school yard grazing against his awkward limbs.  He was better off in goal.  He was better off alone.  The other boys liked Henry because he was silent.  In the world of boys silence is acquiescence.