A Newark police officer was filmed punching someone in May. Correspondent Jelani Cobb asked a police union head if it was justified. Subscribe on YouTube: bit.ly/1BycsJW Their resulting conversation in the new FRONTLINE documentary “Policing the Police 2020” illustrates the debate over use of force in policing: what’s legal, what’s justified and whether those definitions should change. The film is supported by Chasing the Dream, a public media initiative from The WNET Group in New York that examines poverty, justice and economic opportunity in America. Watch "Policing the Police 2020" in full starting Tues., Sept. 15: to.pbs.org/3kgXp2h Instagram: www.instagram.com/frontlinepbs Twitter: twitter.com/frontlinepbs Facebook: www.facebook.com/frontline FRONTLINE is streaming more than 200 documentaries online, for free, here: to.pbs.org/hxRvQP Funding for FRONTLINE is provided through the support of PBS viewers and by the Corporation for Public Broadcasting. Major funding for FRONTLINE is provided by the John D. and Catherine T. MacArthur Foundation and the Ford Foundation. Additional funding is provided by the Abrams Foundation, the Park Foundation, and the FRONTLINE Journalism Fund with major support from Jon and Jo Ann Hagler on behalf of the Jon L. Hagler Foundation.