Sean Williams: Pennsylvania police Taser unarmed black man

An investigation is underway in Pennsylvania following an incident where an unarmed black man was Tasered by police.

Sean Williams can be seen in the video sitting on a kerb and being instructed to straighten his legs or get Tasered - a method used to make sure suspects don't run away.

It appears he is beginning to move his legs as requested, before folding them back again.

The officer Tasers Williams, leaving him writhing in pain as he is put in handcuffs.

The action has been slammed as an overreaction to an unarmed suspect seen to be complying with the requests of officers.

Police were alerted to the scene after they were told Williams was threatening people with a bat, but there no bat was found at the scene, the Independent reports.

Officers allege Williams did not comply with the first officer's request so a second one asked him to sit on the kerb. He was then Tasered from behind. 

After being evaluated by medical staff he was arrested for possession of a controlled substance and public drunkenness.

The mayor of Lancaster, Pennsylvania said she was upset by the incident and she was committed to officers wearing body cams.