Dollman (1991)

"He's the toughest cop on the planet Arturus -- but on earth he's in over his head!"

Brick Bardo is a traveller from outer space who is forced to land on Earth. Though regular sized on his home planet, he is doll-sized here on Earth, as are the enemy forces who have landed as well. While Brick enlists the help of an impoverished girl and her son, the bad guys enlist the help of a local gang. When word leaks out as to his location, and all hell breaks loose, Brick is besieged by an onslaught of curious kids, angry gang members, and his own doll-sized enemies, and he must protect the family who has helped him and get off the planet alive.