1) i thought it used to be both feet on the tryline and that it had recently changed to both feet behind the tryline - no?

2) yes, but I meant can you be penalised for getting within ten yards, even if you don't touch the ball or the player? the example i'm thinking of is chasing an up n under. if you are running at a fullback you may put them off, causing a knock on, without actually touching them or the ball.

AFAIK: It's like being offside anywhere else at the field (at the ptb for instance) – the penalty is only given if you get involved in a tackle or touch the ball (although you see players stood with their hands on their heads to indicate that they're offside and not involved in play far less these days)

You can't be seen to be chasing the kick from an offside position as it puts pressure on the defending player and therefore seen as interfering with play, or you can at least chase the kick to within ten yards of them. I [ithink[/i.

Actually I suspect you may right: when a rife shouts "give him 10, you're offside" chasing players tend to stop 10m away from the receiver – though whether that's to avoid being penalised, or to set up a proper defence line …

That's what I meant by "[ior you can at least chase the kick to within ten yards of them[/i" (covered my bases

)

Not quite. If you are offside and within 10m of a opponent who is receiving a kick you should immediately retire 10m from them. If you don't interfere in play you shouldn't be penalised.