 At the first tournament in 1920 , there were many differences from the modern game : games were played outdoors on natural ice , forward passes were not allowed , the rink was <unk> metres ( the current International standard is <unk> metres ) and two twenty @-@ minute periods were played . Each side had seven players on the ice , the extra position being the rover . Following the tournament , the IIHF held a congress and decided to adopt the " Canadian rules " – six men per side and three periods of play . 
