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Updating the Kos: Batting Average

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By request, sort of, I've been asked to do a post explaining why using batting average should be banned and punished by watching every single one of Tomas Perez' career at-bats. Perez is currently in AAA playing for the Round Rock Express and hitting .263/.293/.378 and the master of pies is 34 years old. You really don't want that do you?

Okay, let's begin with the obvious in a nifty bullet list:

  • Batting average doesn't tell you anything the slash stats don't.
  • What it does tell you is incomplete at best.
  • If it simply repeats info, but not enough to mean something, why use it?

Using batting average instead of on-base percentage is like sending out RSVPs without asking how many guests are in the party. Sure you'll get some idea of how many times the player reaches base, but you're likely missing a big part of the picture. On-base percentage includes hits, batting average does not include walks or hit by pitches or anything else that involves you stepping on first outside of a hit.

For example last year Alfonso Soriano hit .299 while B.J. Upton hit .300. Solely using batting average we assume Upton got on base more than Soriano, but only be a hit or two at most, when we look at the on-base percentages we see Soriano only reached based at a .337 average while Upton did so for a .386 average. On the surface the two are presented as near equals by batting average, but when on-base percentage is implanted into our decision making process we see that Upton is well above average while Soriano is actually below league average despite having a good batting average.

A batter has to get hits in order to have a good on-base percentage, but a batter must also get walks.

But hits are important you say, why yes my Hindu friend, but, and there's always one, slugging percentage will not only tell you if a player gets hits, but, and get this, whether his hits are worthwhile or not. While batting average and on-base percentage are on a 0-1.000 scale, slugging percentage actually extends to 4.000, think one at-bat, one homerun, with the formula being Total Bases/At-Bats we get 4.000.

Jose Vidro hit .314/.381 for the Mariners in 2007, both good, but his slugging was only .394, below league average (around .423). Nick Swisher hit .262/.381/.455, so while Swisher had less hits, he reached based the same amount, and the hits he did have were usually worth more value in bases than Vidro's. There's a misconception that singles don't affect slugging, but they do, here's an example:

Swisher singles in his first at-bat, raising his total bases from 51 to 52 in his 115th at-bat. Old slugging was .447, new slugging is .452. Yes, Swisher's slugging percentage actually went down, but it makes sense when you really think about it: the formula again is total bases divided by at-bats, essentially slugging tells you the average bases gained per at-bat where as batting average treats every hit equal no matter the base value.

A batter has to get hits in order to have a good slugging percentage, but a batter must also get "higher value" hits..

Of course each hit has its own run value, but that's a post for another time, what we're still dealing with is batting average. You've obviously grown accustomed to the scale or tiers of what is a conceived good or bad batting average, which is why I want to encourage everyone to look towards using Equivalent Average (EqA) when attempting to evaluate a batter. You've seen it used around here before, and it's on the same scale as batting average with league average set at .260.

Speaking of league averages I wanted to include these as perhaps a way for novices to grasp what makes a "good" on-base percentage or slugging percentage:

Stat 07 Lg Avg "Good" "Great"
BA 0.270 0.300 0.400
OBP 0.340 0.400 0.500
SLG 0.420 0.450 0.500


Any questions?