These men fight in a mixed nature of both the Celts and Greeks, and are decently armed for their task.
These shock infantry are Celto-Hellenic 'men-at-arms', Celtic warriors of a mixed culture. Celts have long held an affinity for Hellenic society, or at least, certain aspects of it. These men have held more than a slight one though. While they are not of especially great station, they are sufficient warriors, fighting in the Celtic manner, in a motley combination of Hellenic and Celtic gear and dress; long Celtic shields, a Greek helmet, and a Celtic spear and javelins. They soften up an opponent with their javelins and charge an enemy once they're weakened with the great brunt and force of Celtic warriors.
Historically, Celts were at times genuinely fond of the Greeks and their society, though not often so much as to adopt their culture wholesale. However, some did adopt more than others, such as the Celtic graves around Massila and in Galatia with Celtic warriors buried in Greek clothes, with a mixture of Hellenic and Celtic objects, and evidence of Greek-speaking Celts existing in such areas. They would fight for themselves, other Celts, and, in the true mercenary nature of many Celts and Greeks alike, for those who could afford to reward them properly.