Dog laws and question on what to do?

If you are playing in a public park and there is a law sign saying all dogs on leash, then as you are playing soccer a old man is walking with his dog and the dog comes and trys to bite you but leaves slobber on your shorts then you tell the man look what he did and he cusses and says his dogs not responsible and i am 17 years old. Is it ok to call the police and is it ok to beat up the dog and if you beat up the dog and the old man comes to attack you is it ok for me to beat him up to. This happened except i didnt beat up anyone or anything i was so angry and still am so would i be able to call the police