Jim Courier thinks he should:
Among the current top 50, there’s actually a negative correlation between height and first-serve percentage–that is, taller guys make slightly fewer first serves, all else equal–but that doesn’t directly contradict what Courier said. There’s a whole lot that we could investigate in that couple of lines, but let’s stick with the question in the headline.
In the 52 weeks going into the current Miami event, Jannik Sinner made 57.3% of his first serves. That’s the lowest rate of the current top 50, and well below the average of 63%. When he makes his first serve, he wins 74.7% of points–slightly better than average–and on second-serve points, he wins 54.7%, which ranks 11th among the top 50. Altogether, he’s winning 66.2% of service points, again a little bit above top-50 average.
Courier presumably meant that Sinner’s first serve needs to be more reliable, not that he should take something off of it. In the hypothetical, then, he’ll continue to win roughly 75% of first-serve points. He’ll just have more of them.
If Sinner made 65% of his first serves instead of 57.3%, and he continued to win first and second serve points at the same rate, he’d improve his overall winning percentage on service points from 66.2% to 67.7%. That’s equivalent to increasing his hold percentage from 84.9% to 87.1%. (He’s currently holding 83.9% of the time, so he might be a bit unlucky.)
One and a half percentage points–how much does that really matter?
For starters, it would improve his position on the top-50 leaderboard from 24th to 11th. Now, he’s winning service points like Frances Tiafoe and Roberto Bautista Agut. Improved by 1.5%, he’d be in another league entirely, equal to Felix Auger-Aliassime and Taylor Fritz.
Another way of looking at it is within my framework of converting points to ranking places. As a rough rule of thumb, winning one additional point per thousand translates into a improvement of one place on the ranking table. That relationship doesn’t hold at the very top of the rankings, where players are not so tightly packed. But when I first introduced the framework in 2017, the relationship among players ranked 2nd to 10th was that–again, approximately–two points per thousand translated into one place in the rankings.
Back to Sinner. If he won 1.5% more service points, that’s a 0.75% increase overall. (We’re assuming his return game is unchanged.) Call it 0.8%, or eight points per thousand. According to the top-ten version of my rule, that’s worth four spots in the computer rankings.
Sinner is currently ranked 11th on the ATP computer, and after advancing to the Miami semi-finals yesterday, he ranks 9th on the live table. He could head back to Europe as high as 6th if he wins the title. From any one of those positions, a four-place jump would be significant.
Yet the Italian might be better even than that. My Elo ratings place him 4th, behind only Novak Djokovic, Carlos Alcaraz, and Daniil Medvedev. There’s no reliable relationship between points per thousand and ranking places at the very top of the table, but Elo hints at what an elite player Sinner already is. Tack on seven or eight more points per thousand and he might not be the number one player in the world, but he’s right there in the mix.
That is, at least as long as no one else improves even faster. Sinner isn’t alone in his 66.2% rate of service points won. Alcaraz entered Miami with exactly the same number. Sinner has more room to improve his first serve percentage than anyone else at the top of the game, but his rivals will hardly stand around and watch while he does.