This is not a particularly flagrant case given that the guy did attack the cops, but the way in which police in the US behave is outragous. However, I have trouble believing that six able-bodied people could be unable to subdue one man, no matter how big or how fucked up, without beating him with clubs.
In addition, as this article points out, the police continued to beat the man while telling him to put his hands behind his back. Now, anyone with a shred of common sense should be able to understand that by instinct anyone who is being assaulted will use their hands to block it or defend themselves, so no one, let alone someone on pcp, is going to put their hands behind their back if they are being beaten. So, even if these cops acted legally, they need to be fired at once, as common sense should be a requirement for being a police officer.
In many cases, police behavior is excused when it is found that they were acting according to training. This was the verdict in the Diallo verdict a few years ago. The police shot an unarmed man who was committing no crime 41 times. It turns out they acted according to their training and the matter was dropped.
Now, if police training is such that one can act according to it and kill innocent unarmed people, or get someone to put their hands behind their back while betaing them, then clearly needs to be done about the training they recieve.
Personally, taking a cue from Britain, I think the police in urban areas should be unarmed. Taking it a step further I think they should not carry clubs, as I can think of no acceptable use for such a device in the field of law enforcement. mace and stun guns should be more than sufficient, and if a suspect has a gun, a special armed unit could be called in. Barring this, it seems to me that the training police recieve needs to be overhauled completely.