Are pitchers who throw harder better?

A couple of weeks ago we looked at the fact that about half the pitchers who pitched in Major League Baseball throw over 90 miles per hour, but surprisingly, a low percentage of hard throwers are left-handed. This week's question: Does it matter? If you throw hard, does it mean you are better?

Let's look at the average fastball for each pitcher once again. As the miles per hour of the average fastball goes up, does ERA go up, down, or stay the same? Here's the data over the last two years:

It's a clear-cut pattern. We lumped all pitchers below 90 into one group because there wasn't a pattern in that group, but beginning with pitchers with a 90 mile-per-hour fastball, there is steady improvement in ERA as you go up in velocity.

One caller into my Stat of the Week radio segment in Chicago suggested that relievers might be biasing the analysis. Most of the hardest throwing pitchers are relievers, and it's easier for a reliever to have a lower ERA because, quite often, they don't have to pitch a full inning. That's a good point, but we took a look and found the same pattern for starters and relievers: decreasing ERA as velocity increases.

Who are the hardest throwers? They are all relievers except Daniel Cabrera. Here's the top ten list over the last two years:

Zumaya is incredible: over two miles per hour faster than the next fastest pitcher.