Lonnie, I didn't know you run.
Of course, we all do. If you're chased, you run. If you chase, you run. If you gotta be there soon and you're not in a car, you run.
Is running a real sport?
The challenge is simple. "I can be over there before you." In the past it was because a wild animal would eat the loser. Now we just do it so the winners can get shiny pendants on cloth necklaces. (I like the idea of the old style better.)
When do you know you've crossed the line and become serious about running?
It's the same as any other sport. First, you buy shoes. Golf shoes. Bowling shoes. Racquetball shoes. Cleats. Next, you pay-to-play. In most sports this happens very early (golf, bowling.) In running, you never need to pay, the world is your court (all but the watery bits.) So if you do pay to run, yeah you're crossing a line. Other signs include: traveling for an event, recruiting others to play, bragging about your results, (or writing a blog post.) And let's not forget practice.
Well it sounds like anything could be a sport. I buy beer (pay,) "recruit" my friends, travel to a party, and brag when I beat them at beer pong.
Dedicated shoes are a must.