Messages left Thursday with the Fraternal Order of Police weren't immediately returned.
Police Commissioner Charles Ramsey said he supported Williams' decision and said officers need to be very careful in how they use force.
"We have to always be mindful of the fact that we have a responsibility not to overreact," even in tough situations, Ramsey said.
Williams said he felt the misdemeanor charge was appropriate and that the use of force did not rise to the level of a felony, such as aggravated assault.
A disorderly conduct charge against Guzman was withdrawn. Mayor Michael Nutter has apologized to her, saying he was "appalled," ''sickened" and "ashamed" after seeing the video, which went viral on YouTube.