Police were called to a sci-fi convention in Norwich after a confrontation between costumed characters from rival clubs.
Trouble flared when members of the Norwich Sci-Fi Club were refused entry to a fair hosted by the Norwich Star Wars Club at the University of East Anglia.
More than a dozen sci-fi fans from both groups, including some in fancy dress, were involved in the confrontation on Sunday after a member of the Norwich Sci-Fi Club attempted to get an autograph from Doctor Who actor Graham Cole.
It is understood the two groups had been involved in a long-running dispute and the hosts had warned their rivals to stay away after comments were posted on Facebook.
Norfolk Police confirmed that they had been called to reports of an assault.