On Friday, Philly Roller Derby is hosting an anniversary party and fundraiser for member Nina Knockout, who was attacked along with her two children in July. DJ Code Freeze will spin tunes while Philly Roller Derby members past and present and the general public (yes, you&#039;re invited, too!) speed around Philly&#039;s first and only outdoor roller rink. Items will be auctioned off throughout the evening to raise money for Miss Knockout and her children&#039;s recovery. Friday, August 21st, 7 pm-1 am, $3 admission + optional $10 skate rental, Blue Cross RiverRink Summerfest, Columbus Boulevard at Market Street.