What are the best tactics to fight a veteran Khuzait army when you are inferior in Cav numbers, and have a mix of archers and normal infantry? I find those armies very hard to beat on realistic difficulty. I don't have time to even position my troops, as the enemy cavalry comes charging immediately...
1. Use your own cavalry to counter-charge their horse archers right as they being to break to the side to begin their circle. It will cause them to scatter.
2. Anchor your left flank on terrain; buildings and fences work great, large boulders, streams, etc. Set your archers and infantry into loose formation.
3. Pull your cavalry back after a bit and reform. Let your own archers do the grim work they can, while protecting them from Khuzait lancers with your infantry. Don't worry about loose formation getting hurt by lancers; it is better than shieldwall against cavalry due to weapon and unit collision.
4. Repeat the counter-charge against the circle if it threatens to form up again. You have to lead your cavalry yourself for this or be exceptionally good at directing units via F1 movement commands. Using the F3 charge command will make your own cavalry scatter and do dumb **** like death ride into infantry.
Disrupting the circle is key or else your archers will keep turning and not spend time engaging. Horse archers actually have terrible accuracy but tight formations (like shieldwall) help them because they can't miss when it is a solid mass of bodies. Forcing them to fire individually, at individual targets, makes them far less effective.
If you find yourself consistently fighting on terrain with no real terrain to anchor your force, you need to get cavalry of your own though. Fighting Khuzaits on the steppes with infantry blocks is not a long-term winning proposition, unless you can somehow bring so much superiority in numbers that your archers shoot their horses from under them every time.
Alternatively: just stock up on Fian Champions.