Bautista himself claims that the increase in his home run total is due to regular playing time instead of being a utility player (increased confidence), better pitches to hit, and a change in his swing. I am going to mainly focus on the latter: how he could hit so many more home runs by simply making changes to his swing to maximize his strengths and minimize his weaknesses. There are basically two main factors into hitting home runs: hitting a lot of fly balls, and getting lucky (or by getting stronger and getting lucky) by hitting a higher percentage of those fly balls out of the ballpark. The first factor, Fly Ball %, is a hitter by hitter case, as some hitters are ground ball hitters, while other are fly ball hitters. The second factor, HR/FB, is mainly due to luck. Similar to BABIP, a hitter has some control over his HR/FB rate, but it fluctuates around the league average of 10.6% (if you want to read more about HR/FB, you can visit the Sabermetrics Library here).
If you have watched Bautista hit any home runs at all this year, you can see how he has changed his swing. He simply waits for a pitch in one location (almost always inside), if the pitch is not there he will not swing at it, but if it is there he will take an extremely hard swing. As a result, he is sacrificing contact for power (surprisingly enough, he is hitting for a career high in batting average this year). This means that he is very patient at the plate, drawing 98 walks so far this year, and will simply mash any mistake pitch. He has also added a pronounced uppercut to his swing, adding loft to the balls that he hits, and thus increasing his FB%. He has also increased his HR/FB rate this year, either by luck, but also because he is swinging for the fences every time he steps in the batter's box.
What I want to do now is figure out how many of Bautista's home runs this year are from his conscious adjustment at the plate, and how many are mainly due to luck. To do this, I am going to compare his FB% and HR/FB rates from last year and this year, holding one constant while determine how many home runs the other rate contributed (it will make more sense when I introduce the numbers).
The first thing to figure out is Bautista's predicted 2010 numbers based on his past career numbers. Given his amount of plate appearances this year (currently 649, we are going to assume he will get to 675 by the end of the year), we can predict his home runs, FB%, and HR/FB. His career FB% (before 2010) is 42.8% - this means that 42.8% of the balls he puts in play are fly balls (as opposed to ground balls or line drives). It is important to not misinterpret this number as the % of PA that are fly balls - that would grossly inflate his predicted home runs. His career HR/FB rate (again, before 2010) is 10.4%, which is very similar to the league average of 10.6%. So if he were to have 675 PA this year with his average rates, he would hit 19.54 home runs this year.
The next thing to calculate is his predicted 2010 numbers using this year's splits (we could almost use his numbers right now, but there are 8 games left). With 675 PA, and a FB% of 54.8% and a FB/HR of 21.8%, he is predicted to hit 54.08 home runs. In 2010 he has increased his FB% by 12 percentage points (from 42.8% to 54.8%) and his HR/FB rate by 11.2% (from 10.6% to 21.8%). These two increases result in a 34.54 increase in home runs this year as opposed to his career average. The question I want to answer is what percentage of that increase is due to skill, and what percentage is due to "luck"?
To determine how much is due to Bautista's swing adjustment, we want to hold his HR/FB rate constant (keep it at his career average) and set his FB% to 54.8%, his rate for this year. This will show the effect of Bautista increasing his fly ball rate, which is a "skill", without increasing his HR/FB rate, which is due mostly to luck. So with 675 PA, FB% of 54.8%, and HR/FB of 10.4%, Bautista would have hit 25.83 home runs this season. This means that 6.29 extra home runs (25.83-19.54) came purely from Bautista's changed swing at the plate.
To figure out how many home runs came from Bautista being "lucky", we are going to hold his FB% constant at a career average of 42.8%, and increase his HR/FB rate to 21.8%, his rate this year. In 675 PA he would then hit 41.08 home runs, which means that 21.54 more home runs came from his HR/FB rate increasing, which has a lot to do with luck. However, since he has changed his swing to become much more powerful, he would have an increase in his HR/FB rate anyway, but for the purpose of this study we will credit these home runs to luck.
Finally, as you may have figured out from the math, there are a couple of home runs which are unaccounted for. If we take the base of 19.54 home runs, and add the increases of 6.29 and 21.54, Bautista would have hit 47.37. But we previously stated that his projection is 54.08 home runs, so we are missing 6.71 home runs. These home runs are found through the "interaction" term, which is when both Bautista's FB% and HR/FB increase. We can safely credit these to "skill", as I believe that his HR/FB rate has increased because of the change in his swing.
What this all means is that overall, Bautista has hit at least 32.54 home runs this season due to his skill and new swing mechanics, while at most he has hit 21.54 home runs due to luck, although that number is probably much lower. So what he is doing this year should not be a fluke, even if his HR/FB rate drops all the way back down to his career average of 10.4% next year, he should still hit at least 30 home runs. The large majority of his home runs this year have indeed come because of his adjustments at the plate, and possibly because of other intangible measures such as improved confidence and better pitches to hit (although that could be measured in an exhaustive study).
What I would like to conclude is that: a) Bautista's season is no fluke, he should return to the 30 or 40 home run club next season, b) I cannot say that he is not taking steroids, but I can say that they are not the reason he has hit so many home runs this season, and c) this season is going to cost the Blue Jays (or some other team) a lot of money, and I do believe that Bautista has at least a couple more good years left in him. I hope this post clears up at least a little bit of the shock and disbelief at Bautista's incredible season, but it is good to know that there are ways to measure why and how he is hitting all of these home runs.
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