It's better to fight back. Fight back hard. You'll do better in the end, but you'll have to suffer a little for it.

Police are not allowed to break the law. So technically, you could defend yourself if you felt you were being assaulted. But the system is stacked against you.

For starters, in court a police officer's word will be held more true and accurate than yours or anyone else's. There's plenty of evidence to show that witnesses to a crime are horrible witnesses on the stand. The police? They're trained observers. They're trained how to be a witness. A police officer has the advantage on you here, and his word will likely be held as more reliable than yours or any other witnesses.

How do you compete against an expert witness? Lots of irrefutable evidence supporting your side! Of course, any evidence you have, would likely be collected and processed by the police and therefor would likely be "misplaced" (probably in the same place as Hillary Clinton's Benghazi emails) or mishandled in such a way as to make it refutable and no longer valid.

Any evidence in the hands of other witnesses wouldn't be admitted in court. After all, it's easy to fake videos. Hollywood is built around special effects. There's software you can easily/cheaply install on your computer to alter videos. So you can't really trust that cell phone footage captured by the by-stander, now can you? What about their testimony of what they said? A good prosecutor will dig up enough information on a witness to refute their credibility. Many witnesses won't testify. This is true for most cases, but when a cop is involved, do you really think the general public will risk a vindictive police department? If they send that one cop to jail, they'll lose all police presence in their community. It's a risk most aren't willing to take.

The police are experts at collecting evidence. Or should I say, collecting the evidence they need to win their case? So, they'll collect their evidence and of course it'll be allowed in court.

Now, what's the likelihood you'll actually survive a beat-down by a cop? Any cop worth his salt will know it's best to kill you. After all, if you're dead you can't tell your side of the story. When a cop is beating on you, you've only got two choices, really. Don't fight back and die, or fight back and 20 years later in prison by lethal injection.

Short answer: You're dead meat either way. May as well beat the hell out of the cop and live long enough for the justice system to kill you. So in one respect you lose: You're in prison for the rest of your life, and will likely die at the hands of the state. But, for that time you no longer have to work, pay taxes or do anything. Your room and board are covered by the tax payers. You get free medical care. You'll have cred in the slammer for taking out a cop. You'll be king of the prison!