Soccer is probably the most popular game in the world. Many of the best players are from Brazil. The English Wikipedia has a category for them and it includes 4907 pages. Of these pages, 4718 have a Wikidata item.
At the start there were some 527 Brazilian soccer players known to Wikidata. Using this category all the items were made a "human" a "Brazilian" and a "football player". The result is that Wikidata now knows about 4727 "Brazilian soccer players".
Obviously, when the missing items are added, there will be a few hundred more people known to be Brazilian soccer players. When the same process is executed on the category for Brazilian soccer players even more people are likely to be known as such.
Obviously this same process could be done for soccer players from Britain, Russian, the Netherlands, France, Cameroon...
There is enough left to do so join in the fun.