placing yourself between the aggressor and victim while her wounds are attended to = good in my book
placing yourself between the aggressor and his ability to leave the scene = playing cop
as soon as he got in his truck to leave the threat went away. By all means be ready to shoot if he tries to use the vehicle as a weapon, but in california the state will press charges even if the spouse won't, so be a good witness and let the cops do the arresting.
(was hit by a truck as a security guard attempting to stop a robbery when I was 19) we all do dumb "stuff" as young adults, thankfully his dumb stuff didn't land him in jail.