A couple of questions about a frenzied attack. During a Last Man Standing involving Tyros, an engaged gladiator (front) had another opponent come up directly behind, and use the Frenzied Attack.

1. Playing it straight, the defender, a secutor, kept receiving hits to the left shoulder, which has 3 points of mitigation due to shield. He repeatedly mitigated all the damage of several of the multiple (4) attacks.
2. At the same time, the attacker was receiving significant damage from the counter attacks indicated on his card. In the end, the defender received 6 points of damage, and the attacker 7.

We could not find how this should really have been resolved. It seemed odd that the defender, with his back to the attacker, would ultimately deal more damage, or any at all, really. Turning to face the attacker may have made sense, but there's no indicator in the rules for this.

Ultimately, how should a scenario like this play out?