Reese to Police -- I'll Help Bust Your Bad Guy

Reese Witherspoon is more than happy to become the key witness in a case involving a vicious fight between two members of the paparazzi.

The whole thing started in Brentwood earlier today, when two pappers -- not ours -- were trying to get a shot of Reese after she finished exercising. Each wanted to get "the shot" and they began fighting. We're told it was intense.

The LAPD was called to the scene. Cops took a report and are investigating.