I've been following this closely since it happened about a mile from me, and has resulted in widespread protest in our (usually very calm semi-rural) area. Only one deputy fired, not the second one. (The one who didn't fire was a "trainee" for the dept but has several years' experience in law enforcement.) The entire engagement, from the time the deputies stopped the car and started shouting at the boy (from the back) to drop the gun, until they began shooting, took a grand total of ten seconds. The shots were all on the boy's right side except for one on the left bicep, I think. They *said* that as he was turning toward them, his gun barrel raised and the one deputy cut loose, fearing he was about to be shot. However, the entire thing was very rushed, and it seems to me that what may really have happened is that the boy didn't even comprehend what was going on behind him, and as he turned to see what all the commotion was (not even realizing they wanted him to drop his "weapon," which I'm sure he didn't think of as such), the deputy cut him down.
Contrary to what some people have written about this area, it is not at all rife with gang activity. There is some, but the fatalities have mostly been from Vietnamese gangs, not Latino, and they don't live in this area of town. The particular street this happened on is semi-rural and the open field he was in is a place where children frequently play, lacking a close park.
The best word I can come up with for this deputy is "hasty." I can't write the terms I'm thinking to myself here on FR.
Sounds like Mr. Gun Range Expert is in bad trouble for an unjustified shooting resulting in death.