Soul Hackers 2

"on the field" just means not in battle. Once you finish the first two very railroaded sequences, you'll get the tutorial for the sword and that you can knock down the enemies by slashing at them. From here on, you'll be doing quite a lot of this, as it can grant you a bonus attack when starting a battle and unless you're on easy, you'll probably be grinding a bit. Risky enemies (Purple) cannot be knocked down with the sword, but normal (red) and rare (gold) ones can.

Unless you are just walking into things or running past enemies, you should get this no problem before completing the Central Line dungeon (even without clearing Milady and Saizo Soul Matrix 1F)