What are the key differences between a running back and a fullback in football, and how do their roles on the field vary?

A running back in football is typically faster and more agile, focusing on carrying the ball and making big plays. A fullback, on the other hand, is usually bigger and stronger, primarily blocking for the running back and providing extra protection for the quarterback. Their roles on the field vary in terms of running style, blocking assignments, and overall responsibilities in the offensive scheme.