Isn't the skill required what makes it a sport?
All sports require skill.
Most are over all team skill. But golf/darts/pool/darts/boxing etc rest entirely on the skill of a single individual. Either to understand the physics of a drive/putt/shot/throw or how best to attack/defend against an opponent without getting knocked on your own ass.
Also add Swimming as a sports sub genre. My recent sale of Micheal Phelps: Push the Limit forced me to remember that game.
I would suggest just renaming "alternative" to "extreme". I have never heard Skateboarding, BMX, etc labeled as alternative but i feel most if not everyone is familiar with the "extreme sports" title.
Finally
Where do the "arcade" style sports games go?
Hot Shots golf, Mario/Sega [insert sport], Megaman Soccer, Outlaw Golf/Volleball, Nicktoons MLB, NBA/NFL/FIFA Street, Freestyle Street Soccer, etc, etc