I'm sure out there somewhere is what percentage of the time a 3-0 pitch is a ball, called strike, or swinging strike and I would be very interested in those numbers. However, it's pretty obvious swinging at a 3-0 is very much playing against the numbers. And that makes sense to me as a pitcher. Sometimes a pitcher just loses it for a batter for whatever reason. I threw a game earlier this summer in which I only got to one 3 ball count and it was a 4 pitch walk. I knew when it got to 2-0 I was going to walk him because I just couldn't find it. And I've seen this lots of times in my 10+ years of coaching and playing baseball at the high school, college, and amateur level. It just happens.