Which of the following describes an action that is inefficient for a horse's gait?

The action described as rolling is considered inefficient for a horse's gait because it indicates a lack of proper balance and coordination while moving. Rolling suggests that the horse is moving with an irregular motion, which can impair its ability to maintain an even and effective gait. An efficient gait requires smooth and rhythmic movement, which rolling disrupts because it often results in a loss of energy and contributes to fatigue over time, as the horse is expending unnecessary effort to compensate for its unbalanced posture.

In contrast, cross-firing refers to a specific issue where the horse's hind foot strikes the opposite front foot during movement, which can lead to potential lameness and is more about interference than inefficiency of cadence. Overreaching refers to a situation where the hind foot oversteps the track of the front foot, which can also lead to stumbling or strain but is not always indicative of an entirely inefficient gait; it may occur in an otherwise efficient stride. Striding represents a healthy, effective movement pattern in horses, characterized by purposeful and coordinated leg movement that optimizes energy expenditure and performance.

Thus, rolling stands out as the least efficient action for a horse's gait due to its disruptive nature to balance and energy use.