Especially during the last 200m of an 800m race, last 100m of a 400m, etc. Any time when your form starts to suffer because of fatigue and lactate. I tend to pull my arms closer to my torso, tilt my head back slightly, and move my hips back a little. To fix this, what are some cues I could think about while running?
Practice your form in practice. Can't emphasize this any better. When you're hurting it's extremely important to keep your eyes straight and exaggerate the arm swing. Like a sprinter. If your legs are fatigue what's going to help you the most... your ARMS. Also make sure to do pushups to keep your form straight. My coach used to have us do 10x10 the first week and keep adding 10 every week. Take your time and don't rush them.