One of my favorites was last year with UEFA Experimenting with Referee Speed Drills.
I actually received some serious "... you have to be *&#ing kidding me ..." emails on that one. To me it cut both ways. One way was the fact some folks fell for the gag, which was great. The other of course is that they believed that organizations such as FIFA or UEFA would actually do something like that.
Given the history of some of these organizations, I can see their point.
This year I am turning over a new leaf, and wanted to simply share a story about April Fools' Day: 18 Greatest Sports Pranks of All Time from Bleacher Report.
A worthy read on this April Fools.