There surely is little competition in the "hybrid sports car" category and perhaps that's why the pricey BMW i8 took the crown as the #1 seller in that category in 2015.
As Car and Bike explains:
"BMW i8, that made its global premiere in 2013, was recently crowned the world's highest-selling hybrid sports car. Global sales of the Bavarian luxury carmaker's first purpose-built, plug-in hybrid sports car eclipsed the combined figure of all other hybrid sports cars. To be precise, a total of 5,456 units of the BMW i8 were sold last year."
Other potential plug-ins in this category for 2015: Porsche Panamera S e-Hybrid, McLaren P1, Porsche 918 Spyder, Cadillac ELR, BMW ActiveHybrid 3, Acura NSX, Ferrari LaFerrari
"The success of the BMW i8 speaks for itself. It is already the world's most successful hybrid sports car and has comfortably exceeded our own expectations. I can think of no better illustration of the relevance of our young BMW i brand." - Ian Robertson, BMW Sales and Marketing
BMW i8 sales in U.S. – Through December 2015
Regardless of how it's categorized, i8 sales have far exceed expectations, so BMW deserves a pat on the back for that.
Source: Car and Bike