The Serena Williams MasterClass, Rewatched: We Graded the Wrong Half

The first time we worked through the Serena Williams tennis course on MasterClass, we came out with notes on grip pressure, a scribbled diagram of the serve toss, and a mild complaint that most of the drills assume a hitting partner. That write-up was not wrong, exactly. It was aimed at the wrong half of the course. The lessons that have kept their value are the ones we filed as connective tissue between the strokes: the material on what to do with your head before a point, before a match, and in the fortnight before a tournament you have already decided matters.

We went back through it because a specific question keeps arriving in our inbox from people paying an annual subscription fee: is there anything left in a course you have already finished, or did you extract the whole thing on the first pass? For most technique instruction, the honest answer is that you extracted it. For this one, we think you probably did not — and the reason why turns out to be a story about where the tennis world's belief in mental preparation came from, and how much thinner that source is than the belief now resting on it.

The verdict: the rewatch is worth it, but for the mental-preparation material rather than the strokes, and it works less because the course teaches a method than because it shows one athlete's method in enough detail that you can see what parts of it are hers and what parts are portable.

How we evaluated

We should be plain about what this is. We watched the course; we did not go on court and test whether its advice makes anyone better, and no one reading a review should accept that claim from a publication anyway. What we can do is read the evidence around it carefully and tell you where each figure comes from.

Four sources fed this piece. First, the course itself, plus MasterClass's own listing for it — the class dates to 2017, and MasterClass has re-cut and re-titled listings before, so we would rather you check the current lesson count on the course page than trust ours. Second, the published sport-psychology literature on mental preparation, which we read for what it actually supports rather than what coaching culture says it supports. Third, coaching-press reporting on the people who appear in the course, principally Sascha Bajin, whose career after filming is a matter of public record. Fourth, subscriber commentary — the reviews, forum threads, and comparison posts written by people who bought the subscription and are arguing about whether it earns its keep.

Where those disagree, we say so. Where a number is stated by a manufacturer of the claim rather than verified independently, we label it that way. And the whole central argument here — that the mental material rewards a second viewing — is a judgment about a piece of media, not a measured effect. Treat it accordingly.

Where the belief came from

Start with the number everybody repeats. "Tennis is ninety percent mental" is attributed most often to Jimmy Connors, sometimes to half a dozen others, and reliably without a citation. Its nearest ancestor in sport generally is Yogi Berra's line that ninety percent of the game is half mental — which is a joke, and was meant as one. The figure has no measurement behind it. It was never an estimate; it was a rhetorical shrug that hardened into a statistic through repetition. That matters less as trivia than as a warning about the genre: the tennis mental game accumulated its authority by being said often, in a sport whose participants had every reason to want it to be true.

The first serious source is W. Timothy Gallwey's The Inner Game of Tennis, published in 1974. Gallwey was a teaching pro, and his book proposed that the instructing voice in a player's head — Self 1, in his terms — interferes with the body that already knows how to hit the ball. His remedies were attentional: watch the seams on the ball, say "bounce" and "hit" out loud, stop issuing yourself corrections mid-swing. The book has sold in the millions and has been adopted well outside tennis, into business coaching and music pedagogy.

It is also, on its own terms, a collection of one teacher's observations from his own lessons. There are no control groups in it. There is no protocol anyone could replicate. Gallwey does not pretend otherwise — the book reads as a practitioner's essay, which is what it is — but two generations of coaches have cited it the way one cites a finding. The belief is heavier than the beam holding it up.

The second load-bearing source is Jim Loehr, whose Mental Toughness Training for Sports appeared in 1982 and whose between-point work became the most operational piece of mental-game doctrine tennis has. Loehr's account describes studying video of professional matches and noticing that the best players did something consistent in the roughly sixteen to twenty seconds between points — a recovery-and-reset sequence that weaker players skipped or performed erratically. That observation produced the between-point ritual now taught everywhere: turn away, adjust the strings, breathe, choose the next pattern, walk to the line.

We want to be careful here, because this is the point where the history usually gets flattered. Loehr's between-point sequence is a genuinely useful piece of design — it gives a player something concrete to do at the exact moment the match is most likely to be lost. But its origin is behavioral observation of elite players, packaged into a commercial training program by the person doing the observing. That is not disqualifying. It is also not a controlled trial, and the distinction has been quietly dropped in most of the coaching material that cites him.

What the research actually supports

The academic literature that grew up afterward is more modest than the folklore it was recruited to support, and it is worth knowing which parts have held.

Pre-performance routines have been studied fairly extensively, mostly in closed-skill settings — free throws, golf putts, the serve. Stewart Cotterill's 2010 review in the International Review of Sport and Exercise Psychology is the survey most often cited, and as we read it the picture is consistent rather than dramatic: routines help, the mechanism is contested, the studies are small, and the field has struggled to specify what a routine should contain rather than that a player should have one. The evidence supports the shape of Loehr's advice better than it supports any particular version of it.

Self-talk has the cleanest quantitative result in the area. Hatzigeorgiadis and colleagues published a meta-analysis in Perspectives on Psychological Science in 2011 pooling the self-talk intervention studies; the headline effect was moderate — in the neighborhood of a half a standard deviation — with instructional self-talk outperforming motivational self-talk on fine-skill tasks. That is a real finding, and it is roughly the effect size of a decent intervention, not a transformation. Note also what it is not: it is not a study of tennis players under match pressure over a season.

Aidan Moran's 1996 work on concentration in sport performers is the closest thing to a rigorous treatment of the attentional claims Gallwey made twenty years earlier, and its general posture is that the phenomena are real, the popular explanations are loose, and the measurement problem is severe. Nobody has a good instrument for what a player's attention was doing on the third break point of the second set.

So the honest summary is this: the belief that mental preparation matters in tennis rests on one practitioner's essay, one coach's video study turned commercial program, a widely repeated joke about percentages, and a body of controlled research showing small-to-moderate effects on tasks that resemble tennis without being tennis. That is a real foundation. It is a much thinner one than the confidence with which the subject is usually taught.

What the course does that the books do not

This is the part we missed, and the specifics are what convinced us.

The course does not present a mental-preparation method. It presents a person who has one, in situations where you can see it operating, and it does this in places we originally coded as technique instruction. The lessons on the serve and the return are not primarily about the kinetic chain; they are about what decision precedes the stroke and how that decision gets made under a scoreline. Watched as stroke instruction, they are thin — there are better technical breakdowns on YouTube for free, and reviewers who complain about that are right. Watched as decision instruction, the same footage is doing something the books cannot: showing the thing rather than describing it.

Two details anchor this for us.

The first is Sascha Bajin, who appears in the course as the hitting partner. At filming he was, to most viewers, a supporting figure — the guy feeding balls. He had by then spent roughly eight years in that role, through 2015. What happened afterward is a matter of record: he coached Naomi Osaka to the 2018 US Open and the 2019 Australian Open, and was named WTA Coach of the Year in 2018, before going on to work with Kristina Mladenovic, Karolína Plíšková and Donna Vekić. Knowing that changes how the practice segments read. The person on the other side of the net is not a prop; he is the practice condition, and what you are watching is a partnership in which the quality of the opposition in training is treated as non-negotiable. The course never says that. It shows it, and you only notice on a second pass, once you know who he turned out to be.

The second is Richard Williams. His appearance is brief and easy to read as a family cameo. It functions as a source note. The training regime he built for his daughters — including, as he has described in interviews and in his 2014 memoir Black and White: The Way I See It, deliberately introducing noise and hostility into practice sessions so that hostile crowds later would be familiar rather than novel — is the origin of the composure the course spends its later lessons on. The famous long-range plan he wrote before either daughter was born is usually cited with a page count we would not repeat as fact, since the number varies by retelling. But the principle is clearly attributable to him and not to sport psychology generally: rehearse the conditions, not just the strokes. That is stress inoculation arrived at by a parent in Compton rather than by a research group, and it predates most of the literature that would later endorse it.

What the course offers, then, is modeling rather than method. That is a weaker deliverable than a protocol and a more durable one, because a protocol is consumed on first reading and a model has to be reinterpreted every time your own situation changes.

The four sources compared

So does a rewatch justify the subscription

Here is the answer with the uncomfortable part left in.

If you are asking whether there is undiscovered content in the course, no. You saw all of it. Technique instruction is extractive: you take the grip change, you take the toss cue, and the file is closed. Reviewers who report diminishing returns are describing that accurately, and anyone renewing a subscription on the promise of hidden footage is being sold something that is not there.

What changes on a second pass is not the course but the viewer's ability to recognize what is on screen. The Bajin segments mean something different once you know his subsequent record. The father's cameo means something different once you have read his account of how the training conditions were designed. A lesson on serving under pressure means something different after a season in which you lost two matches from a break up. This is a real mechanism, and it is also — we should say plainly — an argument that can justify rewatching anything. Applied loosely it becomes unfalsifiable, and unfalsifiable arguments are how subscription services keep people paying. The discipline we would impose on it is this: a rewatch is worth your time when you can name in advance what has changed in your own game since the last one. If you cannot name it, you are not going to see anything new.

The second, less flattering consideration is price. The mental-preparation content in this course overlaps substantially with a paperback from 1974 that costs less than a month of any streaming subscription, and Loehr's between-point structure is available in cheaper and more operational form in a dozen places. What you are paying the premium for is the demonstration — watching a specific player who won under the specific conditions being discussed. Whether that premium is worth it depends entirely on whether watching helps you more than reading does, and that varies by person in a way no review can resolve for you.

Who this is for, and who it is not

Worth the rewatch if you have played competitively since your first viewing and lost matches you thought you should have won; if you coach juniors and want a visual reference for what practice-partner quality and rehearsed adversity look like; if you already own the subscription for other courses and the marginal cost is an evening.

Not worth it if what you want is technical correction — the stroke breakdowns are shallow relative to free alternatives, and a single session with a competent local coach will outperform them; if you have not played since the first viewing, because the reinterpretation mechanism has nothing to work with; if you are renewing the subscription specifically for this course, which is a poor deal on the numbers.

The clean line, if you want one: the strokes in this course are worth one viewing and the mental material is worth as many as your own game has changed since the last one.

Evidence grade

For the central claim — that mental preparation is trainable and materially affects tennis performance — we grade the evidence Moderate. The controlled research on routines and self-talk is real, replicated, and modest in size; the foundational tennis-specific texts are practitioner observation rather than study; and the most-quoted figure in the field is a joke with no measurement behind it. For our narrower claim, that this particular course rewards a second viewing, the grade is Weak by design: it is a reading of a piece of media, supported by verifiable facts about who appears in it and what those people went on to do, and it should be weighed as criticism rather than as finding.

The myth is that tennis is ninety percent mental and that the mental part can be handed to you in a lesson by someone who has won. The more accurate version is that tennis is a physical game whose margins are decided by attention, that attention is built the slow way — by rehearsing the conditions, not the slogans — and that a course showing someone doing it is worth more on the second viewing than it was on the first, because by then you have finally lost the sort of match it was describing.