#3 looks to be starting to recoil rearwards a little, and pulling his left shoulder back. He still hasnt even started to try and get his gun on target, unless thats just the start. Maybe he was worried he'd shoot his buddies. Either way, the boy on the left still has a good chance of beating him to it. The gunfire is pretty obvious, and you can almost taste the smoke in the air. If you look over their heads, its obvious, there were other discharges.
Lots of "movement" going on there, if you look.
#3 still hasn't started to get his gun on target? If you "look," He has already fired a shot and it thumb cocking it again. That puts him ahead of the curve of the boy on the left.
As for the double ambiguity, sorry I was so subtle. That is the problem with interpreting still image artwork where motion is interpreted, you
might could say. In complex images such as this, you have a LOT going on, but it isn't evident what went on leading up to this or occurring afterwards. #3 may already be retreating. The boy on the left may already be shot for all we know. He isn't using #1 for cover. That was his buddy who is collapsing on the kid on the left, after being shot and turning away for help, but he just isn't going to make it, is he?. The kid caught him and is now defending him from the two attackers.
Heck, it may be that #1 was being chased by 2 and 3 and 3 shot him in the back. Hearing the commotion, the kid on the left heard his buddy being chased and was drawing his gun as his buddy collapsed in his arm, the kid now trying to shoot the attackers.
Many possibilities.