Simplify the following text for a Grade 10 native English-speaking person.
Original: In many minor rugby nations , such as the case of rugby union in Poland , development , has tended to concentrate on rugby sevens as a means of introducing the sport to people .
Simplified: Rugby sevens is the shortened version of rugby union in which only seven players per side feature , instead of the full fifteen . The version of rugby union is very popular , with notable competitions including the IRB Sevens World Series and the Rugby World Cup Sevens .