Accelerate as fast as you possibly can
Separation happens at the beginning
This post explains a tip that I often give to newer players, and I think it's often under-appreciated by many players. The tip is pretty simple: accelerate as fast as you possibly can.
If I want to create separation between myself and my defender, pretty much by definition, the way I do that is to be moving fast when my defender is moving slow.
Changing directions, if you think about it the right way, is also an example of this tip — after changing directions, I am moving fast (in a certain direction) while my defender is moving slow (in that direction—because they haven't stopped running in another direction). But, changing directions isn't always necessary. There's an even simpler way to be moving fast when your defender is moving slow: start by not moving at all, and then IMMEDIATELY START RUNNING AS FAST AS YOU POSSIBLY CAN.
Jogging has its place in ultimate frisbee, don't get me wrong. But overall I think of our sport as one involving periods of slow movement interspersed with moments of running all out, with that switch from slow to fast happening as quickly as we can possibly make it happen.
Why it works
The first thing to note is that playing defense is innately a reactive task. The defense can't run away from you and cover an open space that you haven't cut into yet, because they'll have left you behind and you'll be wide open standing exactly where you already are. So the defense, by definition, has to wait for you to make your move before they react and guard you. In this sense, the offense has a built-in advantage. Defense can only react.
And reacting takes time. That time is where you create your advantage, but only if you use that time right.
Since the defense can only react, there's a huge advantage to accelerating as quickly as possible—as Drake says, going 0-to-100, real quick.
Let's do an example with some quick maths. Imagine you're being guarded by someone with the same top speed as you. Being really naive about it, you might say, they're just as fast as me, so there's no way to get open on them—anywhere I can go, they can be there too. But that's not true. Because the defender has to react, and reacting takes time.
We can use some not-completely-made-up numbers to illustrate the point. Looking at this graph on Quora I found after a quick search, it takes Usain Bolt about 1.5 seconds to get close-ish to his top speed (it takes 15m, and he's moving about 10m/s at that point, so divide the two to get 1.5 seconds). I also found this source from a search for human reaction time, which says that our reaction time is, on average, about 0.25 seconds.
So imagine you are standing next to your defender, and you make a break for it, accelerating as fast as you can:
At 0.0s, you make a break for it. Your defender hasn't had time to react
At 0.25s, you are 1/6 of the way to your top speed. Your defender is finally starting to react to your movement (You are moving faster than your defender).
At 0.5s, you are 2/6 of the way to your top speed. Your defender is 1/6 of the way (You are moving faster).
...
At 1.0s, you are 4/6 of the way to your top speed, your defender is 3/6 of the way (You are moving faster).
At 1.5s, you are at your top speed, your defender is 5/6 of the way (You are moving faster).
At 1.75s, you are both at your top speeds
I bolded the important part. And I wrote it out over and over — for the entirety of that 1.75 seconds, until you have both reached your top speeds, you are moving faster. You are getting further away from your defender. Purely based on the fact that (1) you started first, and (2) it takes a little while for humans to react, you are able to create more and more separation over the course of a couple seconds, until you have both reached your top speeds. And if you both have the same top speed, even after that 1.75 seconds, your defender can't even catch up to you—they can only stay a consistent distance behind.
But this trick only works if you accelerate as fast as you possibly can. If you start jogging before you break into a run, if you don't fully commit, your defender can respond by accelerating faster than you and catching up to you.
There's a nasty cycle that can happen when players aren't fully committed to the cut. I see this especially among newer players. Because they aren't confident whether they'll get open, they don't fully commit to the cut. But then them not fully committing to the cut is the reason they don't get open, because they haven't created the separation that only comes from running as fast as possible, right from the beginning. Instead, you need to fully commit, right from the beginning, and then slow down later if the situation calls for it.
An example
Here's an example. It's not a perfect example, but a pretty good one. Below I've added a clip of NY PoNY against Seattle Sockeye in the 2019 US Open. Keep your eye on Jimmy Mickle, this guy:
The disc comes into play at 1:20:36 on the video. In the course of about 12 seconds, until 1:20:48, Mickle moves maybe 15 feet. He spends some time standing still, some time walking, and some time at a very light jog.
Then at about 1:20:48, he makes a little shimmy forwards, and then breaks towards the endzone at full speed.
In my opinion, there are a few things that make this cut work, but one of the important ones is that he accelerates quickly while his defender is standing still. (You might point out that the shimmy forwards helps by putting his defender slightly off balance, which is true, but, I think this cut would've been successful even without the shimmy.)
The video provides an example of the napkin-math I wrote out above: at 1:20:49, he and his defender are even. Then by the time the clock ticks to 1:20:50, he's pretty much at the maximum separation that he will get from his defender. Between 1:20:50 and 1:20:53, he and his defender are sprinting in sync, except that he's two yards ahead due to the separation that he created in that first second.
In summary:
The defense has to react, and reacting takes time.
Accelerating as fast as you can allows you to get open, even against a defender with the same top speed as you.
Not accelerating quickly doesn't work: the defense can overcompensate by accelerating faster than you to make up for their reaction time
Of course there is more to cutting, and some of the more popular techniques are important, too — like "juking", and "paying attention to your defender's hips", for example. And I think I'll write more about those someday too. But in my experience, too many people worry about "making a V-shape" first, and forget that there's an even more basic theory underneath it: running super fast before your defender has had time to react.
Edit (2022-11-06):
While researching another article, I noticed that Understanding Ultimate has a post here that makes many of the same points. I’m sure I must’ve read that post a few years ago and forgotten about it. My apologies to Benji for accidentally reposting some of his ideas without giving him credit.