Explanation: In the early-mid Roman Republic, the equites were the wealthiest class of Roman citizens who were expected to arm and outfit themselves as cavalry (horses are expensive), when the REPUBLIC was in need of DEFENDING (into foreign lands). They were generally middling riders, as Roman society was oriented around farming and management (typically of farms) rather than professions which required constant practice of horse riding. Horse-riding is something which requires extensive practice to become really good at, so militia/part-time soldiers only really ever become good at it if either they do it regularly in their civilian lives, or if they're a dedicated aristocracy which prides itself on horse-riding. Romans were neither.

When fighting other farming-oriented Italians, this wasn't necessarily a death sentence.

However, by the time of the Punic Wars, Rome fought a larger number of foreign peoples who were much better riders, most notably North African Numidian light cavalry in service to the Carthaginian ('Punic') Republic. Numidians had significant traditions of herding over the plains of North Africa, and significant exposure (and participation in) nomadic societies, and so many of them, even relatively poor men, were 'born in the saddle', so to speak.

Even by Roman admission, Numidian cavalry outclassed Roman riders in nearly every way, and oftentimes, the best Roman equites could do was stall until the Roman infantry prevailed and could come to their aid.