The Rokkaku cop fight skip saves you well over a minute of time for JSRF speedruns. It's tricky to pull off, but with practice you can become fluent at it.

Initially it will take you pretty much 20 sec to do it, but with practice you can cut it down to 5 seconds.

Not really a guide per se, but I made a video which I uploaded to youtube on various players doing the cop fight skip. If you're sloppy at the technique, you want to see if you can optimize your current method, or just want to roughly observe the boundaries of the trigger, check it out here.

In words, basically there's a trigger that if you hit in game, the cop fight will commence. If you play the game the way it was designed, it's unavoidable. The trigger almost entirely isolates a M-sized graffiti you need to spray. However, we (ingenious) speedrunners have outsmarted the Japanese dudes once again- oh yes.

There's a tiny tiny window where you can stand, and just about reach the graffiti without breaking the trigger. You need to approach it very delicately, slowly, and certain angles are preferred. I won't write a thesis on it or anything though, but there are a few things to note.

1. Being a non-dialogue trigger, you can activate it even while airborne (jumping to get off the floor won't stop it from starting the cop fight).

2. You need 3 cans at least, but you'll generally have ~20 so cans shouldn't be an issue.

3. Boost jumping the gap is possible and probably easier but unnecessary.

Here's an image http://imgur.com/uAtyxEo