Here are the Pure Krav Maga Guidelines for Sparring:
Thirty percent of the video has fails for clean defense and counter attack because the counter attack is not meant to be a knock out. Its not a fail problem, but a false reality.
Another thirty percent has a fail because both training partners are trying to do two things to teach each other and to learn one from another. So they try to give a chance to their training partner and increase the difficulty and resistance gradually. Also they try to give their training partner a broad base collection of scenarios.
Many times, once they have a good defense and counter they are happy and don't bother to do the required combination to confuse the attacker enough to facilitate exiting the hotzone safely without interruption.
The reality would be faster. One kick to the balls or one kick to the body balls or stomach followed up with hammer strike to the back of the head or punch to the face.
if you don't want to kill him you might gradually increase the strength of your punches, until its enough to stop him. As
You have people saying you need to cover your face when sparring or defending yourself - I say to them imagine people would be covering their faces when driving a car or flying an airplane... You need to see to navigate to reach and protect all pressure points...
Watch the following Sparring Clips on Youtube to be analysed here!