Television networks have begun placing billboard ads within their telecasts of the NFL, but the league has encouraged them to remove the ads from rotation.

“Small changes in how ads are executed can really add up to how fans perceive games,” says Amanda Herald, VP of media strategy and business development at the NFL.

Billboard ads have been used on television for decades.

“Our industry is changing dramatically,” said Tom McGovern, president of Optimum Sports, a media buying unit of Omnicom Group. “How do you reduce the number of interruptions, so it creeps up engagement in the game?”

Fox has already removed billboards from Thursday Night Football, but continues to have them within their typical Sunday telecasts.

The billboards ads are often value-adds for advertisers.

Regular-season NFL games brought TV networks more than $4.35 billion over the course of just a few months.

“When you tell a client, ‘We are going to take your billboards away,’ it’s not like they don’t think it’s a very big deal,” says Dan Lovinger, executive VP of sales for NBC Sports. “It’s a very big deal.”