Chivalry 2

The best mode I have found to do this on is the 40 player mixed modes. The teams are mixed with a lot of added AI enemies the AI have a lot less health and speed and they are not nearly as hard to fight against as real players.

AI will spawn in the same waves as the players and are very easy to kill as they can be killed in 1 hit by crossbow arrows and any heavy attack from any higher damage weapons. One of the best maps for this is Rudhelm as their are TONS of peasants to kill on top of the players and weak normal AI when you are the Mason team. You can often flank past your opponents and just 1 hit kill these guys with ease. This comes down to my combat tips...

The bastard sword is immediately available for TONS of damage, use this and you will inevitably get the achievement for killing an enemy with a bastard sword who is also wielding a bastard sword.

Upon unlocking use the class you unlock at level 4 with the shield as this will make going against other players easier to block using cn_LT whilst still being able to dish out and take heavy damage including 1 hitting the AI

Combat tips:
1) Pushing your left thumbstick in any direction and pressing will dash you the direction you pressed allowing you to flank opponents or dodge attacks
2) Tapping will deflect incoming projectiles if your timing is correct including melee attacks
3) Holding drains your stamina (yellow bar in the bottom left) which will make it to where you can't block anymore so try to time your blocks
4) While blocking you can counter enemy attacks by using the same attack as your opponent just before their attack hits ( for an overhead which does the most single target damage for a stabbing attack and for a swinging attack which can hit and hurt multiple opponents. Make sure to often switch between these attacks
5) Timing is key in this game, for quicker attacks especially with your swinging attack swing your screen in the direction you want it to hit just about when you press the attack button so it hits sooner. Similar with your other attacks
6) If you just blocked an attack or landed an attack on an opponent you have the timing advantage. If you ever find you don't have the timing advantage, dodge out of combat to reset the fight or successfully block an attack, do not try to attack first if they have the timing advantage it won't often hit first.

Have fun and good luck with your adventures, remember to fight with glory!

You can grind it in offline mode
Play>Offline>Offline Practice and chosse any map (you can also grind the maps specific achivements with this).
Choose the knight class and kill 100 bots, it's easier than in online mode and faster.