I do not know the context of what initiated the encounter.
As for what is on the footage, the Sergeant seems to be conducting himself with a good deal of consideration for the subject and professionalism.
https://www.youtube.com/watch?v=hGQqK9nmPWg
If I was to Monday morning quarterback the incident, the presence of the knife on the floor of the vehicle might have led to a quicker pre-emptive cuffing but the Sergeant did not yet have cover and I can see that he was trying to keep things cool with the subject while he sorted things out and waited for cover. Seems to me that he communicated clearly, and kept up a respectful dialogue while obviously being lied to. I would like to hear what the LEOs on here think.
It is sad to see a young man go down that way. You can really see how bad decisions on his part took on momentum. After making the choice to carry the gun one bad decision led to progressively worse ones as I imagine he didn't want to catch a felony charge on the gun so he ends up shooting at two cops.