The fast push

Kill the wave fast so it crashes into their tower.

From Bronze

Professor Zéphyrinthe Academy's instructor

« Oh, look at that: your wave crashes and your opponent is stuck babysitting minions. Just don't hang around their tower to admire it. »

Their jungler is far
You know where their jungler is: far from your lane. You can push without fearing a gank.
Kill the wave fast
Spells and attacks on every minion: their wave melts, yours stays whole.
The crash
Your wave crashes into their tower. Your opponent has to stay under it and catch the minions, or lose them.
The time is yours
He's stuck on the wave, you're free: back, roam, take a plate or move to an objective.
The classic mistake
You crash, then stay in front of their tower with their jungler unseen: far from your tower, you're an easy gank.

When to do it

You want to back: crash first, and you lose almost nothing while you're gone.
You want to roam or join an objective: your opponent has to stay and catch the wave, or lose it.
Your opponent is gone (dead or backed): crash the wave and take a plate.

Check their jungler first: you'll end the push far forward, so you need to know where he is.
Spells and attacks on every minion: speed is the whole point.
Leave as soon as it crashes: back, roam or move; don't wait in front of their tower.

The classic mistakeCrashing the wave, then staying in front of their tower with no vision: you're the easiest gank on the map.

Good to knowNo fast push when their jungler could be near your lane and you have no vision: you'd be pushing into a gank.

Iron to Silver

Before you back, push. Before you push, look at the map for their jungler.

Gold to Emerald

Every fast push needs a plan: a back, a roam, a plate or an objective. Know it before you start.

Diamond and above

Use the crash to move first: your opponent is stuck on the wave, so you reach the river, the objective or the next lane before him.