I played rugby 7's for a number of years, it is easily one of the most exhausting games you will ever play, if you're not fit, it's pure hell. It utilizes all the same basic rules as 15's except, conversions must be dropped kicked and the scoring team kicks off as opposed to the team that conceded the score. It is definitely a game predicated on speed and skill, it's making it's debut as an Olympic sport in Brazil in 2016. Carlin Isles, a member of the US team and former Olympic sprint hopeful is regarded as the fastest man in 7's,check it out. http://www.usasevens.com/las-vegas/carlin-isles-is-the-fastest-man-in-rugby/