The largest governing body for the sport is the Women's Flat Track Derby Association (WFTDA), with 397 full member leagues and 48 apprentice leagues. WFTDA membership is a major goal of aspiring leagues. Other associations support either coed or men-only derby; the largest organization supporting male roller derby is the Men's Roller Derby Association (MRDA). Within the United States, the Junior Roller Derby Association governs play by those under 18. It modifies the WFTDA rules for minors, such as prohibiting hitting and accelerating into a block. Some U.S. leagues decline affiliation with a national organization because they prefer local governance.