Against aatrox, In team fights, as soon as Aatrox runs in, try to CC him and burst him down first. He is pretty vulnerable to CC and if you can kill him before he gets his combo off, the enemy will lose out on a lot of damage.
 
Try to look for fights when Aatrox doesn’t have his Ultimate or Flash. He will have a much harder time at impacting fights when either of these are on cooldown.
 
Aatrox likes to split push after the laning phase has ended. When he shows in a side lane alone, you could try and start a team fight with his teammates. Have wards on that side of the map though just in case he makes his way to join the fight. Against aatrox, In the team fights, as soon as Aatrox comes into play, try the CC and bring it down first. He's pretty vulnerable to the CC and if you can kill him before you get his combo, the enemy will lose on a lot of damage. Try looking for fights when Aatrox doesn't have his Ultimate or Flash. He'll have a lot more time to hit the fights when either of them are on cooldown. Aatrox likes to split the thrust after the laning phase has finished. When he shows in a single side track, you could try and start a team fight with his teammates.