@johnstitt conventional wisdom would dictate that you should apply ED if Williams is indeed your first choice, even if the numbers are not advantageous (more on that in a minute) because you will relieve yourself of a stressful and unpredictable RD process and you will have first dibs on FA if you apply. My son was admitted ED and it really made for an enjoyable senior year of HS.
So let’s breakdown the ED admissions probabilities for non-athletes. Some base assumptions: 30% of Williams students are athletes and 3/4 of the athletes are admitted ED. That means of 550 entering freshmen, about 123 are athletes admitted ED. Last year, according to the Washington Post, Williams admitted 255 out of 688 applicants (37%). Let’s also assume that the admissions rate among athletes was 100% - these students already went through pre-reads by admissions and were given “offers” via their coaches (in reality there may be a small handful of cases where this process fails). So the ED admit rate of non-athletes would be 132/565 = 23%. The RD admit rate last year was approximately (1205-255)/(9715-688)= 10.5%
So the ED rate for non-athletes is over 2X that of RD. Yes you have an advantage to apply ED! Go for it!