San Francisco Mayor Ed Lee may have given the San Francisco Giants a strange kind of competitive advantage for the 2016 MLB season: visiting teams struggling with tobacco withdrawal. Lee signed a bill into law Friday that bans the use of smokeless tobacco products from all of its sports stadiums, including AT&T Park. The city’s board of supervisors voted unanimously for the ban in April. 

“Today San Francisco entered the history books as the first city to take tobacco out of baseball,” Matthew L. Myers, president of Campaign for Tobacco-Free Kids said in a statement.

Tobacco mostly has been stubbed out at most open-air sports stadiums. Just 11 of the 30 Major League Baseball ballparks have designated smoking areas on site, and smoking has been banned outright in 19 of them. Just 9 of 31 NFL stadiums have designated areas.

 Yet only one park -- Milwaukee’s Miller Park -- currently has rules in place governing the use of smokeless tobacco, and attempts to get it out of players’ mouths have been only marginally successful. In 2011, when it was negotiating a new collective bargaining agreement, Major League Baseball barred its franchises from purchasing tobacco products for its players. Major League Baseball has also banned tobacco products from the minor leagues.

But the players union has rejected proposals that would bar its players from using it, and as long as it’s tucked into their mouths, people like Myers see a bad example.

“When baseball stars use smokeless tobacco, the kids who look up to them are much more likely to as well,” Myers said.

While it’s hard to draw a direct line between one and the other, using smokeless tobacco, or “dipping,” remains a common activity among young people. The Centers For Disease Control and Prevention reports in 2009, 15 percent of high school boys used smokeless tobacco, up 36 percent from 2003. 

But a ban is one thing. Seeing that players abide by it is another. “It's going to be hard to enforce,” San Francisco Giants Manager Bruce Bochy said. “It's a tough habit to break."