The World Series starts tonight in Boston as the Red Sox take on the St. Louis Cardinals. And to networks looking for ad revenue, this live sporting event is the equivalent of a grand slam. 

Today, 70 percent of viewers watch dramas in real time. When it comes to sports, 99 percent watch in real time. Advertising Age’s Michael Learmonth says that attracts advertisers who don’t want viewers to fast forward through their messages. And, as its value to advertisers soar, networks and TV providers are paying more for rights to air live sporting events.

“There are very few comparable events like them, so they’ve retained their value and actually gone up immensely over the last few years.”

It’s also the reason subscribers have been seeing their rate packages jump recently. IHS Inc. research director Tom Adams says cable operators realize sports is the glue keeping their business intact.

“Sports is in an interesting position where it’s the cash cow, but very expensive,” says Adams. “Therefore operators have something of a love/hate relationship with it.”

After all, a quarter of all ad revenue last year came from sporting events.