I too am curious what happened in the Sherlock fandom this week, as it's extremely rare for a fandom that big to show up in the Fastest Growing Fandoms.
I did a quick check and nothing seems odd about the data -- the count matches the count showing on the site, the previous week's numbers were in line with normal growth patterns (it had been hovering around 135k for a bit before that). I even checked locked fic numbers to see if somehow that was playing a role - it shouldn't - but those aren't related either.
So my best guess is either an archive migration (some other fanfic archive porting over fics) or some sort of tag wrangling which brought something else under the "Sherlock (TV)" umbrella. If anybody knows the answer, please tell me!

















