The knocked down kubb is raised in its new position.
This is a perfectly legal and possibly a good strategy. It's used to "rescue" a bad toss from a previous round and might be a good technique to get a better grouping out of a poor previous toss.
If it gets knocked out of bounds, it is re-tossed as a first-time throw (you get 2 throws just like all of the other ones).
For reference, see Section II C, bullet #4,
"4. If a thrown field kubb impacts a previously thrown field kubb then they are
each to be raised where they finally come to rest. It is therefore possible to
knock kubbs into and out of play during the course of throwing field kubbs. It
is important that the field kubbs are not touched by any player until all field
kubbs have been thrown.
(a) This applies to previously established field kubbs from prior rounds as
well; if one is impacted by a thrown field kubb then it is to be raised in
its new position and remains a field kubb.
5. If a thrown field kubb impacts a field kubb in play and the struck field kubb
comes to rest after impact in such a way that it cannot be raised in bounds:
(a) If the impacted field kubb was previously established (having been left
standing in a previous round) then it is to be returned to the attacking
team to be thrown and is treated as if it had not yet been thrown in this
(b) If the impacted field kubb was thrown in the current turn and has only
been thrown once in the current turn, it is returned to the attacking
team to be re-thrown.Page | 7
(c) If the resting field kubb has already been thrown twice in this turn then
it is a punishment kubb (see rules for punishment kubbs Sec II.D.8)."