WFTDA is the Women's Flat Track Derby Association.  This is their most recent patch from WFTDA.  It is only sold to and may only by worn by skaters (officials, coaches, volunteers, etc.) affiliated with WFTDA member leagues.

Note the lack of significant embroidery.  I'm told this patch uses a technique called "micro-embroidery".  The end result is a more durable if less textured patch.