Originally Posted by Sandwlch
Agree, but that is not the explanation. The point is, should there not be a penalty against the attacking player if he takes down a defending player who is legally not moving out of his way? Either it is a penalty to the attacker if the defender moves to obstruct, or a penalty to the defender if, when not moving he is hit and taken down by the attacker. It cannot simply be 'play on'.
You're looking for an empirical answer which in practice is very hard to endorse in this situation.
As a ref my position is :-
Yes. If the attacker takes out a defender deliberately, it would be a penalty.
If the attacker collides with the defender in pursuit of the ball, it would not be a penalty.
The further the kick, the more likely that the defender is colliding deliberately with the attacker if the defender simply holds his ground, as the angles involved to pursue are much less acute, and the immediacy is not present.
However, with long kicks, the defender is much less likely to simply stick in place, he'll almost always chase back, hence collision is much less likely.
With grubber kick chases, the chance of a collision is much higher, especially when the kick is through traffic. Your first focus after a kick is on kicker, to ensure he isn't hit late, however on an attacking kick chase, you have to move focus very quickly to the ball, as a knock on is very possible. It can make it very difficult to assess a collision after the kick, and so unless you are certain that a defender has checked the attacker illegally, or that the attacker has crashed into the defender illegally or tried to contrive a penalty, its play on.
There's also an element of materiality...if the attacker runs into a defending player and takes himself out but leaves the defender standing, I might likely not be bothered with a penalty, but I would give a strong caution on future conduct to the defender. If there was an element of pretending to have been injured I suspect I would penalise, but I've never come across that personally.