The laws only make provision when the ball has gone to ground and is stationary, This case the tackle was not completed and momentum was still carrying him along. Chiefs defender attempted a tackle? Interesting this cause what is the difference between someone sliding before the goal line and the defender sliding in to make a last ditch tackle? Would basically mean the same thing as this incident.
Nope, this was not a tackle, it was a "Law 14 situation"
[LAWS]
LAW 14 DEFINITION
This situation occurs when the ball is available on the ground and a player goes
to ground to gather the ball, except immediately after a scrum or a ruck.
It also occurs when a player is on the ground in possession of the ball and has
not been tackled.
The Game is to be played by players who are on their feet. A player must not
make the ball unplayable by falling down. Unplayable means that the ball is not
immediately available to either team so that play may continue.
A player who makes the ball unplayable, or who obstructs the opposing team by
falling down, is negating the purpose and Spirit of the Game and must be
penalised.
A player who is not tackled, but who goes to ground while holding the ball, or a
player who goes to ground and gathers the ball, must act immediately.[/LAWS]
The problem is that Law 14 applies everywhere in the playing area, whereas Law 15 (tackle) only applies in the field of play, i.e. it does not apply in-goal, and it doesn't mean that you can't tackle (verb) a player in goal, it just means that if you do and even if you bring them to ground, it is not a tackle (noun).
Some sort of Law similar to 15.1 but applying to Law 14 would be useful, and would clear things up immensely
[LAWS]
LAW 15.1 WHERE CAN A TACKLE TAKE PLACE
A tackle can only take place in the field of play.[/LAWS]
Proposed law amendment;
LAW 14 DEFINITIONS
This situation occurs when the ball is available on the ground
, in the field of play, and a player goes
to ground to gather the ball, except immediately after a scrum or a ruck.
It also occurs when a player is on the ground
, in the field of play, in possession of the ball and has
not been tackled.