Is Playing StarCraft a Sport?

I would say no, it's e-sports. There is a difference and rightly so. I do however think it's the future of e-sports and not only Starcraft but games like MOBAs and some FPS games too. Even arena style games like WoW arena and Bloodline Champions have had a huge success in the e-sports scene. And it's only a question of time before more people tune in to WCG, MLG, TSL, GSL etc than any other conventional sport.

Yes it is, Starcraft is considered an E-sport or electronic sports and it's a powerhouse in the competitive Area, other games such as Warcraft's 3 map Dota, CCS, Halo, LoL, between others fall in this category.

As in Sports; players and teams get sponsored by brands and companies such as Sony, Razer, Dell,MSI,and a lot more.South Korea has 3 channels dedicated to Starcraft; own3d streams matches every day 24 hours. I have compete personally on the e-sports scene for ESL.

Only skilled players normally compete on e-sports leagues, skills such as a high APM(actions per minute) are required as in this video: http://www.youtube.com/watch?v=YbpCLqryN-Q

Definition of e-sports according to Wikipedia:

Electronic sports, abbreviated e-sports is used as a general term to describe the play of video games competitively. Other terms include competitive gaming, professional gaming and cybersports. One of the founding fathers of electronic sports leagues is Angel Munoz, founder of the Cyberathlete Professional League.Games that are played as electronic sports normally belong to the real-time strategy (RTS), fighting, first-person shooter (FPS), massively-multiplayer online (MMOG), and racing genres. They are played competitively at amateur, semi-professional and professional levels including in leagues and tournaments.