Sport (as in recreation or as a collective noun) is a funny thing.
Sports (as a group of various physical activities or competitions) are funny (OR funny things).
I wouldn't say that magimagicE is right about BrE. To me it's "sport is" or "sports are". Usually, if we are talking about it in general, we use the singular "sport".
Looking at a few entries in Google, it is only those writers who use "sports" for "sport" that write this way.
That makes it correct.
"Sports" is being used like "maths".
To say this is wrong, you'd have to say that the usage of "sports" is wrong since, in the context, "Sports is ..." is right.
Here are some examples. It appears to be prevalent in Canada and north-east US.
Rock Star Party Ideas • Cheap Sunglasses • Fun Favors Themed
It's hard to argue that 'sports' is plural here: Sports is a funny thing. On one hand, sports can be a unifying factor for otherwise enemies. On the other hand, sports also creates enemies.