Sport - but also it's not quite that simple, because the metric has changed.
It's no longer sales, but player numbers (and also that's outdated - it's 15m+ now), and you can't assume a 1:1 ratio of copies sold to people playing it - because it includes people who bought it second-hand, or have multiple accounts.
Let's say... 60% of people who bought it new played it, averaging two accounts each, while 40% never played it, and 20% of each sold it on to players with the same split (60% played, averaging two accounts each; 40% did not; 20% of each sold it on), a 15m-player playerbase would equate to 11 million copies sold.
Though that's just an example.