Revise sentence and put commas in where necessary.
Some scientists in San Francisco California filmed skateboarders in action.
My answer was:
Some scientists in San Francisco, California, filmed skateboarders in action.
I was wrong - please help by correcting
I know your corrected sentence is right.
There need to be two commas, and you have them -- one after the city and one after the state. No other commas are needed.
http://grammar.ccc.commnet.edu/grammar/commas.htm
See #4.