Ultimate Frisbee Participation [SGMA]

Ultimate Frisbee may not (yet) be the most popular sport, though it had more people playing in 2011 - a trend similar for the past four years.

From the SGMA 2012 Sports, Fitness, and Leisure Activities Participation Report [per RRCA]:

The top three most popular team sports are basketball (24.8 million participants), outdoor soccer (13.7 million participants), and baseball (13.6 million participants). Of the 24 team sports listed, only three of them have had participation gains in the last year – ultimate Frisbee, lacrosse, and gymnastics.
On the other hand, 9 of them have had participation gains over the last four years – lacrosse (+41.8%), rugby (+37.7%), ultimate Frisbee (+20.5%), gymnastics (+18.6%), ice hockey (+15.8%), beach volleyball (+14.8%), indoor soccer (+9.3%), fast-pitch softball (+2.3%), and field hockey (+1.8%).