Tuesday, October 27, 2009

Predicting Batting Average

I'm just coming off my third season of fantasy baseball, and I must say, I'm hooked! I haven't been this into baseball since I was a kid, collecting baseball cards, and watching all the cub games on WGN. It's interesting, in retrospect I now think to myself: "Boy, those stats on the back of the card actually mean something".

Anyway, I've had enough of picking through other people's rankings of players, this year I decided not to let them have all the fun, and I'll do it myself. First up, I'm going to put together my own projections. I know that projection systems exist, but I think it's fun to do my own, making the numbers better match my opinions of players.

So first up, is batting average. Batting Average is one of the more variable stats, and it's based pretty heavily on luck (which is why it fluctuates from year to year). So I don't expect my projected batting averages to be spot on, they will always fluctuate, rather I will try to project something in the middle. I do not have a highly scientific way of calculating batting average, but I'll just go over what I know about it, and give a rough idea of how I make my projections

Batting average is determined by a couple things: BABIP, and strikeout %. Strikeout % is something that's almost completely within a players control, so it's a good stat to look at. Strikeout rate is also something that players tend to improve on as they develop, I generally consider players under 27 still in development, and I'll be more likely to believe in or project improved strikeout rates in those younger players. BABIP is a highly complicated stat that takes into account a lot of stuff, I'll just briefly talk about it. First off, speed is a factor, faster players can post a higher BABIP, because they will beat out more infield grounders. LD%, GB%, FB% are all factors as well, as line drive's have the best chance of landing for a hit (by a long shot), ground balls are second most likely, and fly balls are least likely. So what does this mean? Fly ball hitters post worse BABIP's, and ground ball hitters post better ones. Line drives tend to be highly variable from year to year for most players. Generally speaking, ground ball hitters hit for better average. Anyway, one of the key things about BABIP, is that while it fluctuates a lot with luck, a career BABIP is usually a good indicator of a players future BABIP. That is, unless they suddenly turn from a fly ball hitter, into a ground ball hitter, or vice versa. As players get older, and slower, their BABIP will also fall a little, as they lose their speed. Young players are extremely hard to predict in terms of BABIP, and for that, I found this nifty BABIP calculator tool

Anyway, so to project a players batting average, I first look at their career numbers (BABIP, K%, .AVG). If their career numbers fall in line with what I would expect, then I go with their career batting average for my projection. If, over the course of their career, their strikeout rate has increased, then I will trend their batting average towards the upper end. Since young players can be extremely difficult to predict, I will actually try to predict their K%, and BABIP (using the calculator), and then using those 2 numbers, I hit the fan graphs leaderboard page, and find another player who posted similar numbers, and use his batting average.

There you have it, there's definitely some subjectivity built into my system. I don't expect people to use my projections as the word of god, rather I hope to find that people are interested in/learn from the process I use.

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