FB% And ISO

One of the things we like to do in the statistical community is test common wisdom to see if the empirical evidence lines up with what is believed to be true. One of these truisms is that pitchers are not afraid to high contact slap hitters, and thus will feed them a steady diet of fastballs, knowing the worst case scenario is probably a groundball, even if they turn on it.

Since I’ve been in a graphing mood and we have pitch type stats for hitters on the site, I decided to take a look at this theory, plotting the data from the 121 batters who have racked up enough plate appearances over the last three years to qualify. On the x asis, I put percentages of fastballs seen, and on the y axis, isolated slugging percentage.

Here’s the chart.

As you can see, the data definitively supports the truism. The correlation between FB% and ISO is -.59, suggesting a strong inverse relationship – the higher your ISO, the lower your FB% will be, and vice versa. The average hitter sees fastballs 60% of the time, but that’s the upper bound for low ISO hitters – Melky Cabrera’s .108 ISO and 60.8% FB% are about as far left as you can go on the graph and still be talking about a guy without much power.

However, it’s interesting in that the limit isn’t symmetrical. Notice how there are some high ISO guys on the right hand side of the graph. Matt Holliday, especially, stands out – he’s got a .248 ISO and has still been thrown fastballs 64.8% of the time over the last three years. Coors Field is likely a factor there, but it isn’t with Carlos Lee – .237 ISO, 62.9% fastballs.

Two other interesting players are Johnny Damon and Garret Anderson. They have identical .161 ISOs over the last three years, but Anderson has seen the fewest fastballs of any hitter in the sample (48.9%) while Damon is up near the top (67.5%). Do pitchers perceived Damon as a slap hitter, due to his frame? Or perhaps Anderson just really struggles against breaking balls, and pitchers are exploiting this? Maybe both?

We don’t have all the answers. I’m sure there are scouting reports at play here, indicating some hitters are more vulnerable to bendy pitches than others, but the trend is still clear – pitchers really will challenge no power hitters with fastballs while sticking to their off-speed stuff against the guys who can launch a baseball 500 feet.