I think that would be a hard shot to take even for the ETF. You have curved glass at the front and back of the street car and lots of poles obscuring the view. I believe shooting through glass especially curved is tricky since the bullet loses a lot of energy and can be unpredictable. Even from the side it would be a hard shot because the kid is high off the ground and there wouldn't be an optimal line of fire. A sniper would need a stable platform to take the shot from. The roof of a cruiser or a ladder might do in an extreme pinch, but those are hardly stable.Again, if you can afford to try taking a chance on just wounding him, then I think you should not be shooting at all. He is either an immediate and critical threat to someone's life -- in which case, you can't take any chances, he needs to go down -- or else you have time to try more sober and reserved methods of getting him under control.
If the police DO need to take a controlled shot, as you suggest, they can call in the Emergency Task Force and let them do it with a scoped rifle fired by someone trained in precision shooting.