Weak plantar flexion
When walking, the calf muscle contracts, your foot pushes down, and you are propelled forward.
If your foot is forced up while the gastroc is contracting, you can tear the achilles tendon. A partial tear may be more swollen and sore than weak, while a complete tear is weak. Lie on your stomach with your knee flexed, squeeze your calf, and your foot should plantar flex if the tendon is intact.