LOS ANGELES — Hollywood had a horrible summer.

Between the first weekend in May and Labor Day, a sequel-stuffed period that typically accounts for 40 percent of annual ticket sales, box office revenue in North America totaled $3.8 billion, a 15 percent decline from the same span last year. To find a slower summer, you would have to go back 20 years. Business has been so bad that America’s three biggest theater chains have lost roughly $4 billion in market value since May.

Ready for the truly alarming part? Hollywood is blaming a website: Rotten Tomatoes.

“I think it’s the destruction of our business,” Brett Ratner, the director, producer and film financier, said at a film festival this year.

Some studio executives privately concede that a few recent movies — just a few — were simply bad. Flawed marketing may have played a role in a couple of other instances, they acknowledged, along with competition from Netflix and Amazon.