Chicago police pushing back demonstrators with billy clubs, edited together from a number of videos shot by my companion.  On the front line in the beginning, pretty close to the front towards the end.  This video demonstrates the police maneuvering protesters from the intersection of Cermak and Michigan back West to State, and ends with the CPD sending 10 or so white vans after the marchers who continued South on State as they attempted to head for McCormick Place.  For hot CPD billy-clubbing, set your dial to 5:09 (right up close), and 18:15.
Pretty chaotic at 7:45.  Protesters picking up the barricade at 9:28. 10:35 injured demonstrator coming through the crowd. 15:26 police pushing.  16:48 a little more violent police pushing.  Really nasty push 17:36.  18:35 man yelling badge number of cop allegedly hitting him in back with baton.  18:56 I think a cop hitting a guy in lower portion of frame, but hard to tell.
<a rel="nofollow" class="external text" href="https://www.youtube.com/user/altprint0">Rich Myers</a>
CC BY 3.0
<bdo lang="en" dir="ltr"><a href="//commons.wikimedia.org/wiki/Commons:YouTube_files" title="Commons:YouTube files">YouTube</a>: <a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=KArveRc0W8U"><bdi lang="">NATO demonstration and CPD aggression 5/20/12 at Cermak / Michigan</bdi></a> – View/save archived versions on <a rel="nofollow" class="external text" href="https://web.archive.org/web/*/https://www.youtube.com/watch?v=KArveRc0W8U">archive.org</a> and <a rel="nofollow" class="external text" href="https://archive.today/https://www.youtube.com/watch?v=KArveRc0W8U">archive.today</a></bdo>