This process is common to every pattern of yaksok kyorugi of Taekwondo. It should be settled who is attacker and who is defender. In this photos, the right person is attacker and the left defender.

The attacker moves first. He shifts from Junbi to Apkubi Arae Makgi. Here, the attacker should follow the ways of Samjae. It means he should not draw back, but drop his hip down bending his knee.

And the attacker yells with his motion. It signs that he is ready for atttack. Then, the defender get ready for defence. It means he thinks how he will move. He then yells, which signs he is ready for defence.

Refer to "Understanding the attacker's motion".

Pattern 8 is the following. The technique of counterattack is Yeop chagi.

The attacker shifts from Arae Makgi to Apkubi momtong jireugi with one step forward. Then the defender drops down first, and step aside to the right side with his left hand pushing the attacker's punch slightly, and then, kick attacker's solar plexus with his left foot.

Technical point you should focus on is distance, and keep low pose while kicking.