The "Giant Killer" Effect: What Happens After You Beat Djokovic, Nadal, Federer, Sinner or Alcaraz?
What happens if you bet on the player who just beat Djokovic, Nadal, Federer, Alcaraz or Sinner? How does he do in his next match? Results inside.
Yesterday Jakub Mensik beat Sinner in Doha.
What a surprise.
Mensik played an awesome match, surely the best of his career so far.
The closing odds for Mensik on Pinnacle were around 10.50.
Today Mensik is playing against the Frenchman Fils. The Czech is the favorite and the current odds for him to beat Fils are 1.72.
The Giant Killer study: 247 matches from 2010 to 2025
I remember a few years ago I made a study where I analyzed what happened if you backed or layed the player who had just beaten Djokovic, Nadal or Federer in their next match in the same tournament.
Why? My assumption was that, after beating these players, the market used to price these "Giant Killers" too low in their next match. It was just a perception.
Well, I have updated the numbers until the end of 2025 (from 2010), and I have also included Alcaraz and Sinner.
But I can't include all their matches, as they weren't "giants" from the start. So I have only added matches since each of them won their first Grand Slam — Alcaraz at the 2022 US Open and Sinner in January 2024. That is, they are "Giants" since the won their first grand slam. I think it's a fair assumption.
By 2010, which is where my data starts, Nadal, Djokovic and Federer had all already won several Grand Slams.
And here you can find the results:
As you can see, if you had bet on the "Giant Killer" — the player who beat these 5 players — you would have lost 20.7%! of what you bet, while if you had bet against them, you would have generated a 5.5% positive ROI. Over a total of 247 matches.
Only matches where the next round was in the same tournament are included, and obviously matches between these 5 players are excluded. Flat stakes, Pinnacle closing odds.
What does the statistical test say?
Now let's go to the statistical significance.
Can we say that this positive 5.5% ROI is enough to confirm that betting against the Giant Killers is a winning strategy?
Well, 5.5% looks decent, but the intuition is that 247 bets are not enough to define it confidently as a profitable long-term strategy.
And indeed, if we run a statistical test, this is confirmed. We can't affirm there is value in betting against the Giant Killer, even though historically it has produced positive results.
But we can afirm that betting in their favor is a losing strategy.
The market prices the Giant Killer's odds way below what the true odds should be. As you have beaten on of these top guys, we rate you higher for the next one. It's probably a fair assumption, but it seems than the market goes too far away.
And this is confirmed by a statistical significance test. 247 bets are not much, but the magnitude of the negative yield is so high that the test clearly points to it being a losing strategy.
It can be noticed that this effect hasn't been constant over time. If you look at the chart closely, most of the profit from fading the Giant Killer was generated between 2010 and 2017 — during the absolute peak of the Big 3's dominance.
Why Giant Killers underperform in their next match
OK, now let's go to the causes. Why could this happen?
My hypothesis is that the players who beat these 5 giants might get exhausted, not only physically but also mentally. The player who beats them might get emotionally drained. Also, all the media attention that comes with it could create extra pressure for the next match that the player is not able to cope with.
So according to this, and if we only take this into account, we can say that betting against Mensik today might or might not have value — we don't know.
However, betting on him has probably a negative expected value.
