Many in the USA are not aware of the endless cycle of harassment by the police against young men, especially blacks, such that once you get arrested for a crime, even misdemeanors, you are a perpetual target for the police and the courts, who put you into a catch-22 of paying court costs or having arrest warrants issued for you, but also being turned down for jobs due to an arrest record so that it's impossible to comply with the financial aspect of the legal system's punishment.
I don't know specifically about Garner, but a lot of normal American young men are in this predicament and it seems from the initial reports that Garner, whether deserving or not, was pushed pretty hard by the police. The man who took the video said the cops cared nothing for the circumstances and just targeted Garner and demanded his immediate compliance to their commands, even though he was unarmed and witnesses say he was breaking up a fight and was the good guy in that situation, meaning the police attitude toward him was completely incorrect and biased from him having been "captured" by the system already and essentially put into a treadmill of debt servitude to the courts and their enforcers, the uniformed police, who seem quite willing to use extreme violence without much provocation at all.