When Power Goes Sour: The Bo Jackson Theory

When I was a kid, I was convinced that Bo Jackson was probably the greatest baseball player ever. My friends and I would spend hours working out baseball card trades based around a handful of Bo Jackson cards, arguing over how many Steve Avery cards a "Bo Breaker" card was worth. Maybe it was all the ads Bo was in (Bo knows everything), or maybe it was the hype of a 2 sport star, but we thought Bo Jackson was incredible.

We never worried about stats or actual production, we just loved the idea of a guy who played football hitting home runs and breaking bats on the baseball field. Sadly, as we got older, the numbers became more important to us, and we soon realized that in fact Bo did not know everything. After 8 major league seasons, Jackson too called it quits on his career, taking home his lifetime .250 batting average, 141 home runs, and 841 strikeouts with him.

So, what happened with Bo? He had a couple of good years, plenty of athletic skill, speed, and some power, but he never seemed to put it all together. The same could be said for a lot of other perceived power hitters, too. Why didn't they become the players we thought they were going to be? And how can we tell the "good" power hitters from the "bad" power hitters?

While there's probably no sure way of predicting a power hitter's future success, I want to suggest a few basic stats that are highly indicative of a slugger's future major league success. I call it:

The Bo Jackson Theory

The origins of the Bo Jackson Theory came during an analysis of a childhood hero. Though my memories of Jackson may have been based around an image of a brute strength power hitter, when I began looking at his stats, I realized 2 things. One, he actually wasn't much of a power hitter at all, and two, his strikeout to walk ratio was way out of whack. His lack of success wasn't due to an inability to run or play defense, but simply that he missed a lot of pitches, and even when he did make contact, he usually didn't put much into it. It's a basic concept, and I guessed that if it could bring down the mighty Bo Jackson, surely I could find other examples of power hitters that bombed for the same reason.

So, to test out my theory, first I picked 50 hitters (some still in the minors), and ranked them by their average IsoP at the minor league level. For anyone unfamiliar with IsoP, it is a stat the "isolates" a hitter's power production from his batting average by subtracting it from his slugging percentage. In other words, IsoP is a simple measure for a hitter's pure capacity to hit for extra bases.

Here's the list I came up with for average minor league IsoP.

A bit of an interesting list. I was surprised to see guys like Dale Murphy and Carlos Beltran so low, but overall, I think all of the big name sluggers got into the top 20 or 30. But to be fair, I wanted to also have a ranking system to adjust for each player's age (it's obvious that an 18 year old in the minors is generally going to have less power and a lower IsoP than a 22 year old), so I made up a similar chart ranking each player by their average age at AA ball. Note that some players either skipped AA, played at AA for multiple years, or had some other type of abnormal career path, so I tried to adjust for that.

Obviously, some of the players on the list haven't played above A ball yet, so I approximated their expected age at AA.

Now we have a rank for IsoP as well as a rank for age. The last ranking I wanted to adjust for was minor league strikeout to walk ratio, so I made up one more chart.

Just as with the IsoP ranking, there were a few hitters that surprised me (I didn't realize that Ryan Klesko was such a balanced hitter), but in general it looks like most players are about where they should be. I would agree that Albert Pujols is probably the most disciplined hitter out there, and guys like Wily Mo Pena and Billy Ashley are pretty much the worst.

Alright, so now we've got a rank for IsoP, an age rank, and a K/BB ratio rank. To keep things simple, I took each ranking for each category and averaged out each score (lower scores are better than higher scores). Here's what I came up with.


As with the other lists, there were a few players that I felt were either too low or too high, but I think overall the better power hitters ended up at the top of the list, while the not so good power hitters found their way to the bottom. I could have weighted each category differently and messed with the formula until the list looked better, but I'm really only interested in creating a basic model that everyone can understand that doesn't require much thinking, and is generally accurate.

To ensure that this basic formula is dependable, I took the career home run totals for players on the above charts (I used only players that were either retired or were 35 years of age or older), graphed them out, and then added a linear trend line.

Obviously, it's not a perfect way of evaluating power hitters, but the general trend shows that the idea at least provides us with a range to project future potential. Of the players that either far exceeded or fell short of the trend line, most of them dealt with extenuating circumstances during their career (Strawberry did drugs, Fielder had to play in Japan, McGwire and Canseco did PEDs, Billy Ashley and Jose Oliva both had very short careers with few shots at a starting position).

So, what does the IsoP vs. Age vs. K/BB Ratio formula tell us? Essentially, it says that Bo Jackson was destined to be a very bad power hitter (and in the case of the 50 hitters on our chart, he was the worst). Jackson generally had the lowest power production, worst plate discipline, and was the least advanced in terms of age of all the players on the chart.

When I put it all together, I quickly saw why Jackson struggled so much in the majors, and why he never had a "break out" season. In simple terms, he actually did put all of his skills together and reached his ceiling, it just turns out his ceiling and group of skills never were that great in the first place. And that's why I decided to call this basic approach to analyzing power hitters the Bo Jackson Theory.

Right now, I don't have a true numerical formula for the Bo Jackson Theory, but I'll try to work one out. Then, anyone who is interested can apply the formula to any minor league player and deduce a basic score to analyze their future power potential.

Well, that's it for now. If anyone else has a formula to relate IsoP to plate discipline and age, feel free to post it. Also, please keep in mind that this approach to analyzing hitters is strictly to compare the power potential of each player. It does not take into account on-base percentage or capacity to hit for average. We'll save that for another day.