The attacking team has used up its tackles, they have nothing to lose. If they knock on they lose nothing, yet they still won't put their hands above their heads even though it could lead to a try.
They don't do it because these big tough guys are too scared to expose their ribs and cop a knee there. League just isn't a game that requires courage.
That er.....does happen quite often. Poor you.
Great game. Oh, I'm a born and bred Victorian. Something must be wrong with me....