The principle use of a knife by an unskilled knife fighter is to intimidate their opponent. Thus they draw and display the knife from too far away. This is a very rookie mistake. Trained knife fighters will wait until they have closed the distance to at least their lunge distance before they will display the knife.
One other key indicator of the individual being trained is the way that they point the knife. If they point the knife with the blade oriented up and down, they are most likely untrained. Also, a trained knife fighter keeps the knife close to the body ready to strike, not extended out to the front.
This is a very rookie mistake. Trained knife fighters will wait until they have closed the distance to at least their lunge distance before they will display the knife.
Drawn but concealed wins the element of surprise.