From professional sports through to children's sports at weekends, anybody smoking at an outdoor sports ground could be subject to a fine of up to $300.

"Families and children make up a large part of sporting crowds and for children in particular, inhaling second-hand smoke is even more dangerous because their airways are smaller and their immune systems less developed," Kiama MP Gareth Ward said.

"Sport is all about health and fitness and enjoying time with family and friends. These bans protect everyone from harmful second-hand smoke."

The ban is part of a campaign by the NSW Health department to make outdoor areas, such as sports grounds, smoke-free and make smoking less visible to young people.

Visit health.nsw.gov.au/smokefree or contact the Tobacco Information Line on 1800 357 412.