Given that none of us were at the scene, we needn't judge Smith's actions too hastily. He stated that: "I was trying to perform my job to the best of my abilities given a very difficult, threatening and abusive situation," said Smith.
For all we know, the owner was physically threatening the officer, and in order to take the dog for treatment, he had to subdue or restrain the man in some fashion.
I can imagine that a person who is capable of leaving a dog in a hot car to the point of near death, will not be a very rational, cooperative man.
Perhaps Smith did over react, but unless we actually witness the encounter, we must be careful not to judge an animal rescuer's actions.
Having seen far too many people turn a blind eye to animals' distress, whether in hot cars, in the back of pickup trucks, etc., I am pleased to see that someone has the fortitude to take whatever steps needed in order to prevent an animal from a horrible death at the hands of an uncaring, abusive owner.