Having a bad day is no excuse when you have the full force of the state behind you. Police are authorized to use force if they feel threatened- that means they're trusted to use their judgement, bad day or not. The sad fact is, many cops are bullies and when they get caught like this they need to be dealt with harshly.

here's a link to a similar deformity from the times uk page:

http://www.telegraph.co.uk/news/graphics/2007/03/09/weekpix/070307pig.jpg