I Hate Animal Cruelty [I Am Against Animal Cruelty]

I'm soooooo mad right now...3 weeks ago when I was walking back home from school I saw a dog in front of me I love dogs but I was scared I thought that he was going to attack me since he is a street dog I was so scared so I couldn't move but for some reason the dog didn't move after 2 minutes I decided to come close to him when I got close to him I saw the dog injured he couldn't walk I couldn't take him with me home bc my grandma has allergy of dogs but that didn't stop me from helping him so I decided that on the way to school and way back home I always have to check on him feed him play with him I love him he is really cute and sweet well now I am super mad bc short while ago I decided to go check on the dog when i went to him I saw a man shouting at him scaring him with a bat kicking him I was so shocked and scared bc the man was huge I didn't know what to do so I literally jumped on the man and asked him WHY?!?? He said bc he is annoying and he was scaring his kids he then pushed me and then walked away leaving the dog with bruises he is mean SO MEAN!!!... I brought the dog with me home ...I just couldn't leave him with bruises like that....I don't care if my grandma is going to kill me...do u think what I did is right ? What should I do with the dog?