Knife in-game picture.
|Soldier:||All except Medic, Gunslinger|
|Extra effects:||Fastest Fire Rate|
In terms of damage, the combat knife is outdone by all, even the Stun Baton. Conversely, no other melee weapon can lay strikes on it's opponent quite as often as the Knife can, making melee is the most forgiving when it comes to maintaining the offense on an assailant in range.
Probably a call out to the SFH2 version of the knife, the Custom variant is named the 'First Blood', with a 30% increased chance of a critical hit.