The Saber who had been fighting with Gilgamesh must have fired some kind of Noble Phantasm. Sensing that its magical energy was aimed not at him, but at the sky, Alkeides did not take his eyes off the small threat closing in on him from the front. It was an action born of his refusal to drop his guard against even the weakest enemy.
No.
It was not that he did not look away.
He could not look away.
It was an effect produced by his “mind’s eye.”
It was not instinct.
His accumulated skill and experience, his honed senses, and the flesh and blood that comprised him all dominated his spirit and refused to let him look away.
It was not the other Heroic Spirits he ought to truly be wary of.
It was the lone police officer closing in on him.
Everything he had built up told him so.
The reason why would soon become clear.

Fate/Strange Fake: Volume 5, Chapter 15 ("Gold & Lions II")