Oh well. Another theory up the swanee.

I've always found Hastati rather good in the early game. They have more armour than most light troops and slaughter liby-phoenican levy spearmen in great numbers.

However if they were facing mercenary Pez with a height advantage I'm not too surprised they lost. The Triarii would have been better pinning troops against those. I would probably have gone after their general with more vigour though. kill him and the battle is almost won.