Yet,

In professional writing, it's never appropriate to start a sentence with a conjunction. Conjunctions join sentences. That's their purpose. In creative writing you can do whatever you want and call it stylistic, but not in professional writing. If you want to sound like a reasonably intelligent human being who has been to high school, don't start sentences with conjunctions.

Here's something I just don't understand. If you absolutely must start a sentence with a conjunction because you are unable to construct a complete sentence otherwise or you think you're being artistic, why the hell would you put a comma after it?

I try not to complain about the umpires. Yet, Prince Fielder was clearly out.

Why is that comma there? Seriously. What makes you think you should put a comma there? This baffles me. Of course, you could easily reconstruct these sentences to say:

I try not to complain about the umpires, but Prince Fielder was clearly out.

See how easy that was? Did you put the comma after "yet" to try to make it okay that you used a conjunction to begin a sentence rather than connect two sentences? Is that what's going on here? There's not a logical pause after "yet," is there? I wouldn't pause there. I can find no logical reason to put that comma after "yet." Why do people keep doing it?

I also don't understand why this confusing practice seems to happen most with "yet" as opposed to any other conjunction. Do you more often pause after using the word "yet"? Or perhaps you don't say the word "yet" at all in normal conversation because it makes you sound pretentious, and therefore you have no concept of how to use this word in your writing. 

Whatever the case may be, just stop doing it, okay?