Recently, though actually this has been going for many decades now, there has been a large amount of complaints about police brutality. It has become a lot easier to witness due to readily available video cameras and social media. In the United States, the police has a reputation of being legal thugs and shooting first while asking questions later.
While some incidents are very questionable, our police are actually pretty tame compared to some other countries. Brazil is a country with rampant crime in the poorer areas. and even in the more well off areas. As a result, the police there are aggressive and nobody is complaining.