Goblins are an odd study in group-thought. As individuals, they are sniveling cowards who recoil from anyone who appears remotely stronger than themselves - in large masses, they are known to hurl themselves with unthinking savagery onto pike and axe.

The common wisdom is that in large groups the goblins in front simply have no choice, as they are pushed forward by the teeming masses behind them, and so they fight like cornered animals. From what you have seen, there may be some truth to this.