Now, this is a perfectly legitimate inquiry, one of the most important traits of anyone who want to study any subject is to question “known facts” – and it seems as if I were wrong in trusting my own source without questioning. My argument on the scene can be read in detail below, but the main point was that I identified the warrior with the gorgon head shield as Achilles (based on a reliable source, even as my memory might not serve me correctly at this point). In the end I went back to the sources to investigate the matter further.
There is one important thing to do whenever you want to identify a scene - you need to begin the most general features and work yourself inwards to the details.
Here we see a frieze depicting a dead warrior surrounded by four others fighting over him, and horses being led away at each side. Out of the four warriors, three have crested helmets and one a shield decorated with a gorgon. The scene also (not seen here) depict several gods in two groups facing each other.
There's also a context to take consider: a pediment depicts the Delphic competition and the other two preserved friezes a gigantomachy and (most likely) the judgment of Paris.
The setting is therefore, as should be expected, from myths and legends. The reasoning should thus be something like this:
The two groups of gods staring at each other are probably representing two factions of some kind. On one side we see Ares, Apollo, Aphrodite and two other gods while we have Athena, Hera (?) and another god at the other side. The two groups are unfortunately broken off by a lost section. We can thus be sure that this part of the frieze depicts the gods during the Trojan war (The former group helped Troy, the later the Greeks).
I would argue that the front frieze should be considered one unit and the depicted battle would in that case be one of the many fights for the body and armor of a fallen hero. But who?
There is only one thing that can help us in the identification (remember, I am very much not an expert on the Iliad) and that is the gorgon shield. This figure is normally identified as Achilles, as everyone want him to be represented in any frieze, but (and this is what brought up the question to begin with) Achilles shield is described in detail in book 18, lines 478-608 of the Iliad and there is not a word about any gorgon. Rather the opposite, the shield is described as depicting the whole world.
My first thought was that this then was the shield he used to have before the death of Patroclus, but that can't be correct as the warriors are supposed to fight over Antilochus body - and he is killed after Patroclus (not even in the Iliad itself)
So it's not Achilles. Who then? I only remember one warrior who owns a shield decorated with a gorgons head and that is Agamemnon himself. This is unfortunately as far as I can come right now as I can't remember all the fights that Agamemnon took part in during the epic, I'll be back on that later on.
In the end, my interpretation of the scene is still one of the Trojan war, but the only identified warrior is Agamemnon, not Achilles. Then again, there might very well be evidence that I am unaware of (such as inscriptions, literary accounts or written names).