who did amasawa fight before fighting horikita and ibuki together

Amasawa was attacked by Shiba before the Horikita-and-Ibuki fight scene. The information tied to that matchup indicates her earlier injury came from Shiba, not from Horikita or Ibuki.

What that means

• The later clash with Horikita and Ibuki happens after Amasawa was already hurt.
• That earlier encounter is the reason some readers notice scars or damage during the fight scene.

Context

In fan discussions, this is usually brought up when people ask why Amasawa looked injured or less than fully fresh going into that confrontation. The common answer is that Shiba was the one who fought her beforehand.

TL;DR: Shiba fought Amasawa before she faced Horikita and Ibuki together.