Question about a dogs behavior...

[xFire Angelx]

hey guys!
well theres a pit bull 2 doors down that is the most adorable doggie ive ever seen... i dont know a lot about dogs... ive only had dogs when i was little but i dont even remember having them.
ok down to business... the dog well she/he looks well trained and everything but when anoth dog comes around and she/he is outside she/he goes CRAZY growling and barky and lunging for the dog about 30 minutes ago i saw the pit bull doing that to a tiny little dog like a weener dog... now she/he was tied up so she/he couldnt get to the little walk that was being walked but there have been 2 times in the past 3 weeks that ive seen the owner chasing after her/him because it got loose.. should i be worried about this dog? i mean is it a potential danger seeing as how the dog reacts with other dogs around? the sun is coming out its getting warmer theres a dog park about 10 blocks down so theres dogs all over the place around here... should i be worried this dog if it gets loose will go after another dog? i dont want any animals getting hurt and honestly i dont think the dog would hurt a human but i havent seen anyone but the owners pet her/him so i dunno.
any advice?

-Sarah