My understanding, without regard to WI statutes, is that the right to self-defense can go back and forth during an altercation.
For example, let's say that Kyle DID point his rifle in a provocative way at somebody.
That might justify Rosenbaum attacking Rittenhouse.
However, as soon as Rittenhouse runs away from the altercation, then Rosenbaum is not longer justified in attacking.
The unjustified continuance of an attack by Rosenbaum then allows Rittenhouse to claim self-defense.
If, prior to the shooting, Rosenbaum had turned around and begun walking away from Rittenhouse,
then Rittenhouse would no longer be justified in an act of self-defense.
Good point that the defense should have pointed out.