https://www.indymedia.co.uk/en/2012/09/500684.html

 https://www.indymedia.co.uk/images/2012/09/500686.jpg

 https://www.indymedia.co.uk/images/2012/09/500687.jpg

These images are from the RT (TV) news coverage of the massive Madrid demo on Sept 25. The first image (1:36 into the Youtube video) shows 2 undercover cops, wearing jeans and black-bloc style hoodies, dragging a protestor along the ground by his arms. The hoodie on the left then drops the protestor's right arm, as a helmeted and truncheon-carrying riot cop takes over, grabbing the protestor's leg (2nd and 3rd images). Another cop joins in as they continue dragging the protestor towards the police van (4th image). Then the 2nd undercover cop rejoins the 1st hoodie (as picked-out by the blue light), both helping the uniformed cops to complete the arrest (5th image). Click on the images to enlarge. You can see the full sequence within the original video here -

 http://www.youtube.com/watch?v=vZ8yNywAOEk