When you meet Chadley in Chapter 3 of Final Fantasy VII Remake, he provides you with the Assess Materia, which allows you to learn about an enemy’s weaknesses, resistances, and how to best defeat them in combat. It’s all apart of his research. He needs your help in gathering up battle intel reports, and one of the tougher ones is The Stagger Effect Part 1.
You need to use unique abilities on a staggered enemy and charge your ATB gauge 10 times. To do this, you first need to find a strong enough enemy to withstand your party’s attacks while you fight to stagger them. The best way to stagger an opponent is to use a weakness on them, use Cloud’s Focused Thrust ability to increase an enemy’s stagger bar, and focus on attacking more durable enemies in combat.
The unique abilities for this battle log require you to hit a target using any of your abilities on a character. For example, when you have a character in a staggered state, you have a set amount of time to hit them for even more damage than you usually would. To capitalize on it, you can use Cloud’s Braver or Focused Thrust ability to hurt them even more. After you use an ability, you then have to charge your ATB up, which you can do with basic attacks. You need to do this 10 times.
You likely won’t be able to finish this battle log during Chapter 3. You need to progress through the story to work on it, and you can return to Chadley at another time to turn in the battle report to receive your reward, which is the First Strike Materia.
There are plenty of battle intel quests for Chadley you can do in Final Fantasy VII Remake. Make sure to visit the battle intel page to see if any new ones arrive and learn what type of Materia you can earn for completing them.