What task/effect is aimed at upsetting an enemy's formation or tempo to cause them to attack in a piecemeal fashion?

The task aimed at upsetting an enemy's formation or tempo to cause them to attack in a piecemeal fashion is accurately described by the concept of disruption. Disruption involves actions designed to interfere with the enemy's operational effectiveness, which can lead to confusion within their ranks and a breakdown of their coordinated efforts. By causing the enemy to engage in isolated or uncoordinated attacks, friendly forces can exploit the resulting vulnerabilities and gain a tactical advantage.

In contrast, diverting focuses on redirecting the enemy's attention or resources, which may not necessarily break their formation or tempo. Defeating refers to the complete destruction or incapacitation of the enemy's capabilities, which is a more final outcome than merely causing temporary disruption. Deceiving involves providing false information to mislead the enemy, which does not directly aim at upsetting their current operational flow or tempo. Thus, disruption is the most appropriate term for the described military tactic.