Knife vs. Sniper
If you are far away from the sniper and plan to kill with your M9, run in a zig-zag pattern but maintain a more or less straight run towards him/her.
Once you are up close and personal with the sniper, don't waste any time slicing and dicing. Snipers have a nasty tendency to pull a trick lag shot out of their rifles right before you're about to finish them off. Lessen the likelihood of being "one shot killed" by staying behind the sniper and aim towards the head/torso. If you do not stay on the flank, he/she may very well resort to no-scoping you. Snipers are the easiest projectile weapon opponents. Be prepared for a loss however, because lag can make your opponents shoot you even when it appears you're not in front of their rifle.
Knife vs. Auto
One of the hardest ways to knife someone, however much praise and amazement will be shown if you succeed. If you are going to try this, jump around randomly and land as many hits as you can on the head/torso. Again, getting behind them unnoticed is your best bet; aim for their head first so you put a nice dent in their HP. If you're lucky, your opponent will run out of ammo before you die and you will then have an easy time earning your payback.
Knife vs. Auto Reloading
Run at your opponent, and aim for the chest and head. Do not allow your opponent to put distance between you and him/her. Knife without mercy. Do not panic or your reaction time will dull and your knife blows will not hit your desired target points. The more blows you get before the enemy moves away, the faster and more likely you are to committing a knife kill.
Knife vs. Pistols
The most dangerous to face are the Beretta and M945 because they have a high magazine capacity. Another pistol to be concerned about is the desert eagle because it packs a punch of about 50 HP per hit. Remember to close the distance of your opponent. Snipers and Pistol users usually count on long and medium distances, respectfully, to kill the enemy; with exception to close combat sniping. If you're facing a Glock23 or MR-73, relax and tease them a little bit like a cat about to decapitate a mouse.
Knife vs. Shotguns
Be wary of Desperados and Benellis because they have a faster rate of fire than Remingtons. With Remingtons, try to stay in sync with rearm times so you know when your opponent is about to pull the trigger and in turn jump out of the way in time. Remember, just two well placed blows to the head/torso can easily knock him/her dead.
Knifing Awards
The two unique in-game awards achieved by killing someone with the M9 are "Slash" and "Head Slash" (much like its "Head Shot" counter part). Neither award earns you any extra points; however, they demonstrate your knifing prowess to other gamers, especially in an all out weapon match.
Double Kills, Multi Kills, and Special Forces are all very possible with the knife too!
Overview
It's the one weapon everyone in Soldier Force has.
Hardly anyone uses it in combat (because no one knows how), ironically.
It is more difficult to kill with; thus more skillful.
Can take down opponet in 2 slashes.
Sometimes safer to use in combat than reloading.
Speed increases when equipped.
Many minigames use the M9.
Slash timing must be flawless.
Now go knife someone.