So What is Fault Tolerance, Anyway?

“Fault tolerance” is a term from computing – it refers to a machine’s ability to remain functional even in the face of a fault, a small problem. For example, imagine that one of the transistors in your processor fails. Is your entire computer going to crash? No, because your computer is fault tolerant; it can tolerate the fault, the transistor failure, and still function.

Elite forehands are also fault tolerant. They can tolerate small inaccuracies in preparation, timing, or execution without failing. This fault tolerance is an essential ingredient of a high level forehand. To gain a maximal advantage in tennis, our goal isn’t just to produce the best possible result. Rather, it’s to develop a stroke which produces that best possible result with the highest margin for error out of the widest array of different situations.

Success Under Imperfect Conditions

If a particular stroke only produces a fast, heavy, accurate shot when struck perfectly, but when struck imperfectly, frequently results in an outright miss, that shot is useless in an actual match. The shot is not fault tolerant, because it can’t handle a fault, a small mistake preparation, timing or execution, and still succeed.

Federer hitting a swinging volley, a shot where fault tolerance is extremely important
Roger Federer hitting a swinging volley – a shot for which it’s very difficult to establish a consistent contact point, and thus fault tolerance is essential to success.

On the other hand, a stroke which succeeds even in the face of a small preparation or execution mistake is fault tolerant and is competitively useful. This idea is critical to the rest of our discussion.

Only fault tolerant strokes grant a competitive advantage, because during stroke production, conditions will never be perfect. We’d all like to be in perfect position for every shot, and to practice enough that we never mistime our swings, but in practice that’s impossible, especially if the other player is elite.

Instead, we’re going to hit many of our shots while slightly out of position, and make many small timing and execution mistakes throughout the match. This takes some humility to admit, but, as usual, humility is a useful virtue. To win, our stroke needs to succeed in spite of these small mistakes.

There are two basic classes of skills, two critical steps in your stroke development, that are required when learning an elite forehand. The first is developing quick feet and proper movement so that you can avoid ever having to hit out of position, and avoid ever mistiming the ball. The second is building in enough fault tolerance that you can hit out of position and mistime the ball.

Tennis is Often Difficult and Awkward

Federer hitting an inside-out forehand that he didn't quite get around, but because his stroke is fault tolerant, the shot succeeds
Roger Federer hitting a forehand on which he didn’t quite get around the ball, and it’s too close to him. The shot succeeds, and he still wins the point.

When two players are competing, each is doing everything in their power to make the other’s shots as difficult and awkward as possible. Therefore, the most advantageous competitive strokes are the strokes that still function at a high level out of difficult and awkward positions.

We see this concept at play all the time on the tour. Professional players constantly slightly mistime their strokes, and they constantly hit shots while slightly out of position. Everyone is moving so fast and hitting so hard that it’s humanly impossible to position for and strike every shot perfectly.

Of course, every player tries to hit every ball perfectly, and they move so well that they actually do hit a lot of them pretty perfectly, but in the end, even the ever graceful Roger Federer hits the occasional mistimed forehand, or gets caught by a solid, deep return and has to hit out of position.

Of course, because he’s Roger Federer, that out of position or mistimed shot almost always still goes in.

Rafa’s Forehand – A Fault Tolerant Masterpiece

Rafael Nadal possesses what is probably the best example of a fault tolerant forehand in all of modern tennis. Like every player, Nadal often slightly mistimes his forehand. Rafa’s stroke, though, is so fault tolerant that you can barely even tell these shots were mistimed. Sometimes, his ball will drop a little shorter in the court than normal. Other times, it’ll drift a little wider than average. But as a spectator, you barely notice, because even when Nadal slightly misses, the resulting shot still keeps the point neutral.

Nadal showing his mechanically sound, fault tolerant forehand on the red clay
Rafael Nadal’s fault tolerant forehand on display on the red clay – hips rotated, core stable, wrist relaxed.

On offense, when Rafa slightly mistimes or mishits the ball, half the time it just lands on the line for a winner instead of landing inside the line where he was aiming. Sometimes, sure, he hits it back towards his opponent and the rally continues in neutral, but even that isn’t all that bad of a miss. Where other players mishit the ball out and lose the point immediately, Rafa mishits the ball in and just has to start back over from neutral, so he still wins about the half the points he plays after those offensive “misses.”

For Rafael Nadal to miss to the point where his opponent actually gains a significant advantage from that miss, he has to really miss. He is so strong, his hips are so engaged, and his wrist is so loose that is his forehand is the poster child of fault tolerance – he makes a small mistake in timing or preparation, and the most common outcome is that the rally continues like nothing happened.

Why Fault Tolerance is so Essential

Rafael Nadal is also amazing at digging out balls that land right at his feet. Heck, sometimes he even rips an inside-out winner off of that shot. No player goes into a rally wanting to play a shot off of their shoestrings, but sometimes, you’re forced to. This is why fault tolerance is so essential to high level tennis. If your forehand only works when in perfect position, you’ll never be able to compete with players that can frequently put you in imperfect positions.

The shadows at the Gerry Weber Open in Halle are criss-crossing the stadium, impairing visual information and making fault tolerance essential to success
At the Gerry Weber Open in Halle, Germany, the shadows from the stadium obscure the court during the final between eventual champion Roger Federer and runner-up David Goffin.

Imperfect positions are inevitable. Here’s another example – what about when the lighting on court gets weird? At Halle every year, the shadows on the court get ridiculously distracting. Every player’s ability for precision declines, at least a little bit, playing in conditions under which their brain is simply receiving less quality information from their eyes. Yet, as we watch these spectacular rallies taking place across the criss-crossing shadows in Halle, the players… still barely miss.

How is that possible?

It’s possible because a tour level player’s stroke is so fault tolerant that this small fault – the fact that they aren’t getting perfect visual information – is completely tolerated by the stroke. Their stroke is resilient enough that the small amount of stress placed on the system by the imperfect lighting isn’t enough to have a significant effect on its results; when they slightly mistime their swing or slightly mishit the ball due to the lighting, their stroke still succeeds.

So How do I Develop Fault Tolerance?

Fault tolerance comes from technique. There are ways to hit the ball that are fault tolerant, and ways to hit the ball that aren’t. From your feet, all the way up through your legs, hips, chest, arm, wrist, and hand, each body part has a job to do to strike the ball in a fault tolerant manner.

A correctly taught stroke is not a complicated series of limb positions and joint angles to memorize.

Don’t be scared off by that list of body parts, though. It makes fault tolerant strokes sound complicated, but they actually aren’t – in fact, simplicity is one of the primary drivers of fault tolerance. A correctly taught stroke is not a complicated series of limb positions and joint angles to memorize, but rather a few static positions to learn and a few volitional movement patterns to execute out of those static positions.

One of the keys to fault tolerance is eliminating extraneous movement and extraneous tension from your body. Every muscle that isn’t driving force should be relaxed, and every movement that isn’t adding racket head speed should be scrapped. We build our strokes up from the essentials, from the parts of the swing directly responsible for generating racket head speed, and strip away the non-essential parts of the swing that don’t help it, but can definitely hurt it if not executed perfectly.

Fundamentals and Fault Tolerance Come First

At Fault Tolerant Tennis, we focus on the fundamentals of each swing that create the swing’s fault tolerance. The few aspects of elite swings like Rafael Nadal’s forehand that are directly responsible for their unparalleled consistency and quality.

Daniil Medvedev's unique high takeback and loopy backswing; because this doesn't interfere with the fundamentals, his swing is thill fault tolerant
Daniil Medvedev has a uniquely high take back and loopy forehand swing, but since it is fundamentally sound, it’s still extremely effective.

This website is your place to learn those fundamentals. Each article, be it on the forehand, the serve, movement, strategy, or coaching, focuses on the core aspects of that concept that are universal across all high level play.

Occasionally, when discussing something like the forehand, we’ll wade into some personal preference optimizations, like Juan Martin Del Potro’s looping backswing, or some non-harmful (for those players) personal idiosyncrasies, like Medvedev’s uniquely spacious backswing, but mostly we will discuss the core fundamentals that every world class forehand shares.

Our goal is to distinctly and clearly separate stylistic choices, which vary greatly from player to player, from the foundational, biomechanical principles that are universal among all elite strokes. There are many great ways to hit a forehand, but they all share certain crucial traits.

Those traits are what we focus on here, as they are the traits that create hard, heavy, fault tolerant strokes.


  1. Ian Mak
    February 21, 2021

    Great instructions- logical & effective. Please clarify – racket 90 -135 degrees to forearm…. I can’t seem to figure out how tues is positioned. A photoshot will help please. Thanks.

    1. Johnny (FTF)
      February 23, 2021

      Glad it was helpful! As for the 90-135 degree angle, two things. First, I’ve updated the image on our “Two Rules that Govern Every Shot” article to show the angle we’re talking about.


      Second, you can go on YouTube and pause any video of a forehand – Fed, Rafa, Novak – any of them, at the end of their backswing. You’ll see their racket and forearm 90 degrees from each other. As they twist forward, their racket naturally lags behind their hand, and then whips around their forearm, all while that angle remains (opening up a little, but non volitionally).

  2. Poida
    July 21, 2021

    So in other words, the wrist is loose and moves freely but the racket/forearm relationship of 90-135 degrees integrity must be maintained? It seems the wrist plays a role in getting this relationship or am I mistaken?

  3. herve kergrohen
    May 7, 2023

    Thanks for your book and website that I studied in great details. I worked on your tips playing against the wall. I noticed that the attention to contact and angle helped keep the ball on the same side of the wall and repeat the shots in a very consistent way. I struggle first with the notion of “angle” and it would be helpful to provide more images (which angle?). Your advice on the shoulder tilt is extremely helpful, I tested it at training with my usual partner and it helps 1. do the unit turn 2. get the ball higher and longer especially and not only on low balls 3. get a lot more spin and then force the high ball to hit the ground before the line This has surprised my partner who had to get back to reach a longer and higher ball with more spin (above shoulder and he is really tall). I watched several pros in slow motion and they all do it. Thanks

    1. Johnny (FTF)
      May 8, 2023

      Awesome. As far as the shoulder angle, Alcaraz (who was barely on tour when I wrote the book) uses it heavily – it’s one of the reasons he hits so high over the net and so heavy. When I write the second addition, discussion of his game and his forehand will certainly be a part of it.

      As far as angle, I believe you’re referring to “string angle?” I’m referring to the angle of your string bed when you hit the ball. Is it parallel to the net, slanted down, or slanted up? That’ll change the shot you produce.

      1. herve kergrohen
        May 12, 2023

        Tilt is great! Maintaining the “string angle” is also fantastic for regularity in many positions. I have incorporated it with zero problem, it is very confortable. I noticed that maintaining the string angle implies a good unit turn, which lengthens the path at the fixed angle. In my first message, I asked about the “angle between racquet and forearm”. I asked because I developed a pain in the cubitus side of the wrist when I started and I believe this was because of trying to maintain (force) a wrong “racket-forearm angle”. I have now returned to my previous angle which is more natural to me and anyway within your recommendations (90 to 120). Playing against the wall helped a lot to fine-tuned the changes. On the court, it is really positive, less effort, more length, regularity and, hence, more tactical possibilities, really. Thank you!!!


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