I grew up on a horse farm... I punched a lot of horses. And it generally worked for those few nasty horses that tried to bite, kick, etc. I also bit a few. And, yes, it mattered where you punched them. Between the eyes was pretty stupid. Hard as a brick.
Down at the teeth got your message across. And I never had a horse try and bite me again after biting them back. One particularly nasty nag (Sand) used to try and kick the shit out of me every time I entered his stall. I finally broke a horse-shoe rasp over his hind quarters... I still use the halves for wood shaping. He never kicked at me again. We had an understanding. Horses are smart that way. (he gave me the worst kicking I ever received, too... right in the chest with both hooves. Just because I was walking behind him. Shoeing him was a chore... until after I broke the rasp on him. Then he calmed down and let me shoe him. But Sand was a nasty, ill-tempered, bastard roan and was the closest I ever came to shooting a goddamned horse...
All that said, punching a police horse is retarded. And hope that the Philly PD ensures that idiot gets some serious assault charges. Police horses are trained to a degree that is amazing. They don't need 'coaching' as it were. To make the grade as a police horse... is an animal in the top .001 percent of the breed.
But you grow up on a horse farm and you've punched a horse. Guarantee it!
Cheers,
Sirhr