Rittenhouse testimony. Joshua Ziminski was the first person to engage prior to seeing Rosenbaum.

Apparantly everybody was so distracted by Rittenhouse breaking down immediately following this part.
That noone is pointing out that according to Rittenhouse testimony and consistent with the first shot fired. Ziminsky was also the first to engage Rittenhouse. Armed with a pistol pointed at Rittenhouse and then rittenhouse dropped the fire extinguisher and then Rosenbaum tried to attack from behind, as Rittenhouse tried to flee. Which Ziminsky then instructed Rosenbaum to get him get him get him get him and then fired the first shot.