Minus 7.3: The Number Behind Purton’s 80 Winners That Nobody Mentions

Halfway through the season, a simple question — how many wins should each jockey have had? — produces an answer few expected.

Written by AI · Prompted by a Human

This article was researched and written entirely by an LLM (Large Language Model, a.k.a. AI). Sohil Patel provided the data, guided the analysis, and prompted the conclusions. The AI wrote the full article in under 2 minutes.

EIGHTY WINNERS. Through 485 of approximately 850 races this season, Zac Purton sits atop the Hong Kong jockey premiership. The number commands respect. It should.

But here is another number: 87.3.

That is how many winners the betting market expected Purton to ride — based on the odds of every horse he sat on when the gates opened. Eighty wins this season versus an expectation that he should have won on nearly 88 mounts puts him at underperforming by more than seven winners. The biggest deficit of any jockey in Hong Kong this season. Dead last on a table few talk about.

Now look at the top of that same table. C L Chau. Twenty-eight winners from an expected 20.7. Plus 7.3.

Same number. Opposite sign. The premiership leader and the man outperforming his opportunities by the widest margin — separated by the mirror image of 7.3 wins.

How Expected Wins Work

The idea is simple. Take the market odds of every horse each jockey rode this season and calculate the implied number of wins — after adjusting for the track take. For the sake of this example, we leave the track take aside to illustrate the concept. A $2.00 favourite has a 50 per cent chance of winning. Ten rides on $2.00 favourites, five expected wins. If you win on six, you are one win ahead of what the market expects. If you win only on three, you are two winners behind. Add them all up across the season, compare the total to actual winners ridden, and the difference tells you who is winning more than they should — and who is winning less.

The Problem With Raw Numbers

Consider Ka Ying Rising. Five starts this season, five wins. His highest starting price? $1.05. At those odds, the horse was essentially a walkover with a saddle on it. Any jockey aboard was collecting.

But Ka Ying Rising is not the only short-priced winner inflating the tally. Purton won on Little Paradise at $1.35, Super Strong Kid at $1.45, Bulb General at $1.50, and Invincible Ibis at $1.55. In total, 15 of Purton’s 80 winners this season came at odds shorter than $2.00 — rides where the market had already done most of the work before the gates opened.

Expected wins strips that noise away. It asks a harder question: given the quality of your rides, are you winning more or less than the opportunities warranted?

For Purton — so far this season — the answer is less.

The McDonald Test

Here is where it gets interesting. James McDonald rode Romantic Warrior four times this season. The prices? $1.05, $1.10, $1.40, and $1.55. All four won. Add Gold Patch at $1.55 and McDonald had five sub-$2.00 winners of his own — a higher proportion of his 16 total winners than Purton’s 15 from 80.

Yet McDonald sits at minus 0.2. Dead level. Almost to the decimal.

If riding short-priced horses was enough to explain the deficit, McDonald should be deep in the red too. He is not. The market gave both men cheap wins. Only one failed to bank enough of the harder ones.

Who Is Beating The Market?

Start with what Jerry Chau is working with. His shortest-priced winner this season was Flying Wrote at $2.30. Not a single sub-$2.00 walkover. No Ka Ying Rising. No Romantic Warrior. Where Purton’s longest-priced winner paid $13.15, Chau won on Celtic Times at $35.10, Healthy Happy at $22.15, and Lucky Twin Stars at $17.90 — horses the market had all but written off. He is not padding the scorecard. He is picking locks.

Chau is not alone in outperforming. D B McMonagle and M F Poon both sit at plus 3.7 — finding winners the market did not expect. Andrea Atzeni and Hugh Bowman, each at plus 3.2, are delivering more than the odds suggested from their respective books of rides. Jerry Orman at plus 2.5 and Y L Chung at plus 2.4 round out a group punching above their weight.

At the other end, the drop-off below Purton is steep but not solitary. Brenton Avdulla at minus 6.8 — eleven winners from 17.8 expected — is the second-biggest underperformer among the regulars. Matthew Chadwick at minus 5.0 and Karis Teetan at minus 3.8 fill out a bottom three that may surprise those following the premiership table alone.

Then there is the middle — jockeys landing almost exactly where the market put them. C Y Ho at dead level. Lyle Hewitson one-tenth of a win below expected. Harry Bentley, three-tenths. If you believe the market is efficient, these riders are confirming it.

The Full Table

Jockey	Exp Wins	Actual	+/−
C L Chau	20.7	28	+7.3
D B McMonagle	5.3	9	+3.7
M F Poon	15.3	19	+3.7
A Atzeni	26.8	30	+3.2
H Bowman	33.8	37	+3.2
J Orman	14.5	17	+2.5
Y L Chung	11.6	14	+2.4
E C W Wong	17.1	19	+1.9
L Ferraris	20.1	22	+1.9
P N Wong	4.2	6	+1.8
H T Mo	2.3	4	+1.7
M L Yeung	10.6	12	+1.4
J Moreira	0.9	2	+1.1
W Buick	0.2	1	+0.8
R Moore	1.3	2	+0.7
C Y Ho	24.0	24	0.0
C Demuro	0.1	0	-0.1
K Yokoyama	0.1	0	-0.1
L Hewitson	20.1	20	-0.1
J McDonald	16.2	16	-0.2
K C Leung	16.2	16	-0.2
R King	0.3	0	-0.3
H Bentley	18.3	18	-0.3
C Soumillon	0.4	0	-0.4
M Barzalona	0.4	0	-0.4
C Williams	0.5	0	-0.5
C Lemaire	0.7	0	-0.7
U Rispoli	0.7	0	-0.7
M Guyon	16.0	15	-1.0
H Doyle	6.7	5	-1.7
D Probert	3.0	0	-3.0
K De Melo	3.0	0	-3.0
R Kingscote	11.3	8	-3.3
A Badel	19.3	16	-3.3
K Teetan	26.8	23	-3.8
M Chadwick	16.0	11	-5.0
B Avdulla	17.8	11	-6.8
Z Purton	87.3	80	-7.3

Season data through 485 of approximately 850 races. Visiting jockeys with limited engagements included for completeness.

What This Is Not

This is not a verdict on Purton’s season. Eighty winners at the halfway mark is elite by any measure. And the market is not infallible — odds can be wrong, and a jockey who consistently draws tough barriers or poorly-rated horses may see expected wins inflated by factors beyond their control.

There is also the matter of market bias. Popular jockeys attract popular money. When Purton sits on a horse, the public bets it — and that weight of money pushes the odds shorter than they might otherwise be. Shorter odds mean higher implied probability, which means higher expected wins. If Purton’s mounts are systematically overbet by punters who follow the name rather than the form, his expected tally of 87.3 may itself be inflated. The market’s faith in the champion may, paradoxically, be the very thing that makes his numbers look worse on this table.

Then again, McDonald is no stranger to public money either. And his numbers land dead level.

On Sunday at Sha Tin, Jerry Chau rode his 200th Hong Kong winner. Plus 7.3.

Zac Purton leads the premiership by a mile. Minus 7.3.

∎

About the Author

This article was researched and written entirely by an LLM (Large Language Model, a.k.a. AI). The AI wrote the full article in under 2 minutes.

About the Prompter

Sohil Patel is a Hong Kong racing handicapper based in San Francisco who focuses exclusively on HKJC racing. Unlike most punters who rely on publicly available form guides, Patel maintains a proprietary database of curated datasets spanning multiple seasons that allow him to find systematic edges in HK race betting. He spends more time than he should prompting LLMs.