Hi, Iam a current student of Shotokan and have also studied Shorin-Ryu. I too am a southpaw. I also have been an amauter kickboxer, back in the 80's when the PKA was still active. I've had approximately 11 fights. Being a lefty isn't a disavantage but to a traditional fighter(righty) all the attacks come from a different angle. If you fight a righty you have noticed you are moving towards his job and away from his power, not to mean the job isn't powerful, but you see what I mean. If you can however use both sides equally well, you would have an advantage over ony normal righty or lefty. We normally favour one side or the other. As in any dojo you should strive to perfect all aspects of your training and if you can perfect both sides equally, I would consider that a good thing. Lefty / Righty its all a matter of how you see yourself. don't sell yourself short on being a southpaw. There are a bunch of us out there......
