Back testing, how many games to be statistically relevant?

[venture]

Does any one have opinions or links to how many games do you need to say that your theory is statistically relevant?

I back tested a theory and it went 123-87 from 08-11. So 210 games at 52.5 games per year. Is that enough to have any confidence in it this year? It hit 58.6%, best year was last year 30-18, 62.5% worst year was 7-6, 53.8%

[M.W.]

You need to look into the concept of z scores to determine how likely that the outcome you have observed would occur by random chance.