I may sound like a broken record here, but I think something akin to the basketball rules about jumping players would be useful to think about for these situations, and with small amendments, they could be made to apply equally well to both a player who has just kicked the ball ahead and is running with an intent to jump to contest the ball, and a player who is on the non-kicking team who also wishes to contest the ball. It could also be made to apply to the situation here; a player kicking when an opponent is trying to charge down his kick.
33.6 A player who is in the air
a. A player who has jumped into the air from a place on the court has the right to land again at the same place.
b. A player who has jumped into the air from a place on the court has the right to land on another place on the court provided that the landing place and the direct path between the take-off and landing place is not already occupied by an opponent(s) at the time of take-off.
c. If a player has taken off and landed but his/her momentum causes him/her to contact an opponent who has taken a legal guarding position beyond the landing place, the jumper is responsible for the contact.
d. An opponent may not move into the path of a player after that player has jumped into the air.
e. Moving under a player who is in the air and causing contact is usually an unsportsmanlike foul and in certain circumstances may be a disqualifying foul.
33.6 b would have to be modified to remove the red text part because we have obstruction laws.
33.6 c would have to be modified because we have tackle laws.
Essentially, when the ball is thrown (or in the case of rugby, is kicked), the player on the kicking team who jumps to contest the ball owns the space he will land in, unless someone is already there, in which case the player already in that space owns it.
One of the arguments against this that I often hear is that there are only 10 basketball players on the court while there are thirty on a rugby field. and it would be difficult to manage. However, the basketball court is much smaller too, and in fact the density of players on a basketball court is higher. Also, basketball umpires are not out in the middle like a rugby referee, they stay close to the sideline.
So,
1. When a player jumps, and his landing space is empty, any opponent moving into that space is responsible for the collision.
2. When a player jumps, and his landing space already has an opponent standing there, the jumping player is responsible is he clatters the opponent in that space.
3. When a player is trying to charge down a kick, the player kicking the ball owns the space in which he is standing.
