There are few things in football that divide a crowd like a stuttered penalty run-up. Half the ground thinks it's clever. The other half thinks it's cheating, or at minimum bad manners. And a certain kind of former player will be on television within an hour explaining that in their day you just hit it.
The rules on it are actually quite clear and the tactical logic is sound. Whether it's a good idea is a more interesting question.
What's allowed
The relevant law permits feinting during the run-up. What it prohibits is feinting after completing the run-up — that is, the final stutter as you're about to strike is illegal and results in a caution and a retake, or an indirect free kick if the ball goes in.
The distinction is where the run-up ends, which is a judgement call, which is why these decisions cause arguments. In practice, the accepted version is a hesitation somewhere in the middle of the approach, with a continuous final two or three steps.
Why it works, when it works
The mechanism is straightforward. A goalkeeper facing a penalty has to commit before the ball is struck, because reaction time doesn't allow otherwise. He's timing that commitment against the taker's approach — the rhythm of the run-up tells him roughly when the strike is coming.
A stutter breaks that timing. The keeper either commits early, in which case the taker can see which way he's gone and place the ball in the other corner, or he waits, in which case he's late and covers less ground.
Against a keeper who dives early, the stutter is close to a free goal. You're converting a guessing game into a shooting exercise with a stationary target.
Why it fails
Three problems, and they're all real.
Modern keepers have adapted. The counter is simple: stay up, don't commit, and if the taker is looking at you to see which way you go, then don't go anywhere until the ball is struck. A keeper who genuinely holds his position defeats the stutter completely, and now the taker is striking a penalty from a broken rhythm with no advantage gained.
It compromises your own technique. This is the underrated one. A penalty struck from a smooth, rehearsed run-up is technically consistent. One struck after a hesitation involves a different approach speed and a different plant, and takers who stutter miss the target noticeably more often than those who don't.
The referee might not agree with you. If your stutter is judged to be after the run-up rather than during it, you've turned a penalty into a booking and a retake at best.
The version that actually works
Having watched a lot of these, the successful ones share a feature: the hesitation is early and the final approach is normal.
The taker slows or pauses around three or four steps out, then completes the run-up at normal speed with a normal plant. The keeper's timing is disrupted but the striking mechanics are unchanged.
The version that fails is the one where the taker is still slowing right up to the ball, taking tiny steps, essentially standing over it before poking it. That produces weak, mishit penalties and it's also the version most likely to be penalised.
The psychological argument against
Here's the case that I find most persuasive, and it isn't about technique.
A penalty is a task under enormous pressure. The single most useful thing a taker can do is reduce the number of decisions he has to make. Pick a corner before you place the ball, walk back, run up, hit it. Nothing else.
A stutter run-up introduces a decision into the middle of the process — am I going to hesitate, when, how long, and am I now watching the keeper or looking at my target? That's cognitive load at exactly the moment you don't want any.
The takers with the best long-term records tend to be the ones with the simplest routines. Not always, but the pattern is there. Whatever else is true, consistency of process seems to matter more than cleverness.
The etiquette question
Briefly, since it comes up every time. Is it unsporting?
I don't really think so. A penalty is a contest between a taker and a keeper, and the keeper is allowed to jump on his line, wave his arms, delay, and talk. Deception within the rules is a normal part of the sport — a body feint by a winger is exactly the same category of act.
The objection seems to be aesthetic rather than moral. It looks like showing off, and if it fails the taker looks foolish, and there's something in football's culture that finds premeditated cleverness distasteful in a way it doesn't find spontaneous cleverness.
Which is fine as a taste, but it isn't an argument.
What I'd advise
If you have a reliable technique and a preferred corner, don't stutter. You're introducing risk for a marginal edge against keepers who have mostly learned to ignore it.
If you're the kind of taker who watches the keeper and chooses late, then a modest early hesitation is a sensible part of that approach and you should practise it until the final three steps are identical to your normal run-up.
What nobody should do is stutter occasionally, on instinct, in a shootout, having never rehearsed it. That's the version that ends up in compilations for the wrong reasons.