Batting average and ERA
May 6, 2005 12:50 AM   Subscribe

BaseballFilter: now that spring is here as well as baseball, I need an explanation of how to calculate batting average and ERA. Do outs (pop flys) count in your batting av? Foul tips? And ERA: is it the average only of batters that score a run, and not just hits? What about a relief pitcher with someone on base who scores--does that count?
posted by zardoz to Sports, Hobbies, & Recreation (13 answers total)
1) Yes in that it lowers your batting average
2) No, unless the foul tip causes the batter to strike out
3) Yes, hits do not count toward ERA
4) No. Relief pitchers can inherit runners, but if those runners come in to score, it does not count toward the relief pitcher's ERA - it affects the ERA of the pitcher before them who put those runners on base. Hope that clears things up a little.
posted by fishbulb at 1:00 AM on May 6, 2005

The MLB has a guide to some of the most basic stats.

The important thing to remember about Batting Average is that only At-Bats count. So sacrifice flies and bunts, walks, fielder's choice, hit-by-pitch, errors, etc. that don't give the batter an at-bat don't count toward the average. Other statistics like On-Base Percentage and OPS take all plate appearances into account.

Full gory details below.

Here are the relevant definitions from MLB's full stats page:
At bats
A batter is charged with an at-bat when he makes an out (unless credited with a sacrifice bunt or sacrifice fly), or reaches base on a base hit, on a fielding error or on a fielder's choice. A batter is not charged with an at-bat if he is credited with a walk or hit by pitch, or reaches base on catcher's interference.
Base hit
A batter is credited with a hit when he reaches first base (or any other base) safely on a ball hit into play in fair territory, after it touches the ground or a fence before being touched by a fielder, or which clears a fence, and when the fielder could not retire the batter with ordinary effort.
Batting average
Divide the number of base hits by the total number of at bats.

Earned runs
The total number of earned runs allowed by the pitcher. An earned run is a run for which the pitcher is held accountable, and shall be charged every time a runner reaches home base by the aid of a hit, sacrifice bunt, sacrifice fly, stolen base, putout, fielder's choice, base on balls, hit batter, balk or wild pitch (including a wild pitch on third strike which permits a batter to reach first base) before fielding chances have been offered to put out the offensive team. In determining earned runs, the inning should be reconstructed without the errors (including catcher's interference) and passed balls, and the benefit of the doubt should always be given to the pitcher in determining which bases would have been reached by errorless play.
Earned run average
The total number of earned runs allowed by the pitcher, divided by his total innings pitched, multiplied by nine.

posted by stopgap at 1:40 AM on May 6, 2005

Just to add a little bit to the very good responses above. A pop fly does not count as an at-bat and doesn't affect your batting average if it is considered a sacrifice fly. While determining when a sacrifice fly occurs is usually a subjective determination by the game scorer, it usually occurs when a batter's fly ball results in a runner advancing a base.

And just to be clear, hits are irrelevant for ERA calculations, though of course there is a correlation between hits and runs. But, for example, if a pitcher walks four batters straight, resulting in a run, his ERA would increase even though no batters have gotten hits.
posted by EatenByAGrue at 2:12 AM on May 6, 2005

To clarify the matter of 'foul tips': If it's fouled into the air and caught for an out, then it counts as an at-bat. That includes foul tips into the catcher's mitt when there are already two strikes.

Other foul tips would not end the batter's plate appearance, so would not count as an at-bat.

Unless, as in the other day, when Renteria fouled a bunt attempt with his finger, and had to leave the game. I know his replacement inherited the strike, but was Renteria charged with an at-bat?
posted by Kirth Gerson at 4:10 AM on May 6, 2005

Another small detail when calculating ERA (which, again, is the number of earned runs divided by innings pitched, multiplied by nine): if a pitcher doesn't complete an inning, each out counts as a third of an inning. So if a pitcher pitches six full innings and is pulled out after striking out one batter in the seventh, for the purposes of ERA calculation he pitched 6 1/3 innings.
posted by Acetylene at 6:09 AM on May 6, 2005

Kirth, when was the game that Renteria left in the middle of an at-bat? I'm looking for the box score to confirm my suspicions, but I think that it is his (Renteria's, in this case) at bat if it an out, but the batter at the time gets credit for a hit or a walk.
posted by LouMac at 7:19 AM on May 6, 2005

BTW, true baseball nerds prefer WHIP over ERA.

WHIP=Walks + Hits / Innings Pitched

Basically, it tracks how many people, on average, you let on base each inning. It comes down to which pitching performance you consider worse: someone who loads the bases but gets 3 outs before anyone scores (WHIP = 3), or someone who gives up a solo HR (ERA = 9). It's also more meaningful for tracking the performance of relievers, who have shorter, more intense outings.

Good starters keep their WHIP under 1.2. Good relievers are under 1.0.

*goes back to checking the fantasy waiver wire...*
posted by mkultra at 7:23 AM on May 6, 2005

Note that, in ERA calculation, it is in fact possible to have an infinite ERA:

Say a pitcher is called up from the minors to fill a relief role in the bullpen. The first time he's put into a game, he faces one batter, who hits a home run. He's immediately taken out of the game, and is sent back to the minors after the game, never to be brought back up again (this sort of thing has happened, probably a lot). He didn't retire a batter, so he officially pitched 0 innings, but he was charged with an earned run, and 1 divided by 0 is infinite.

As for what happens when a batter is replaced in the middle of a plate appearance, as happened to Edgar Renteria, the rules say this:

If the batter leaves with two strikes, and the replacement batter strikes out, the original batter is charged with the strikeout. If the replacement batter does anything other than strike out, including walk (even if the original batter had a three ball count), the replacement batter is charged/credited with the action.

If a pitcher is relieved in the middle of a batter's plate appearance, the rules are slightly different: If the batter had two strikes on him and strikes out, the original pitcher is credited with the strikeout. If the batter had three balls and walks, the original pitcher is charged with the walk. If anything else happens, it's credited/charged to the relief pitcher.

There are all sorts of crazy situations one can find in baseball. I remember a year or two ago, when B.J. Ryan of the Orioles got credit for the win in a game in which he never threw a pitch. How? He came into the game in the bottom of the eighth with the score tied, two outs, and a man on first. He then proceeded to pick the runner off first for the third out without having thrown a pitch to the batter, thus ending the inning. The Orioles then took the lead in the top of the ninth, and Ryan was replaced for the bottom of the ninth. Since he was the pitcher of record when the team went ahead, he got the win, but never actually threw a pitch.
posted by cerebus19 at 7:34 AM on May 6, 2005

true baseball nerds prefer WHIP over ERA

I think fantasy nerds prefer WHIP. Does it correlate any better to success than ERA? My pitching metric is ERA+, but that's not really calculable until the season is over.

And just to confuse things: sacrifice flies do count in calculating OBP, so it's possible to have an OBP that's lower than your batting average.
posted by yerfatma at 10:20 AM on May 6, 2005

While determining when a sacrifice fly occurs is usually a subjective determination by the game scorer, it usually occurs when a batter's fly ball results in a runner advancing a base.

Actually, I believe this was once the case, but no longer. To be scored a sacrifice fly (and thus not an at bat), the runner must score, not just advance a base.
posted by mookieproof at 10:52 AM on May 6, 2005

Just to add to my previous comment:

It's actually possible, though unlikely, for a pitcher to walk a batter he didn't pitch to:

Jones pitches to Smith, and throws two strikes, then three straight balls, for a 3-2 count. On the third pitch, he injures himself and has to leave the game. Baker is brought in to replace him. The opposing manager knows that Smith doesn't hit Baker well, so he takes Smith out and puts in Carter. After his warmup tosses, Baker pitches to Carter and throws ball four, walking Carter. By the rules, Carter receives credit for the base-on-balls and Jones is charged with the walk since he threw the first three balls, even though Jones never pitched to Carter (at least, in that plate appearance).
posted by cerebus19 at 1:08 PM on May 6, 2005 [1 favorite]

I must say I'm somewhat surprised that nobody's brought up the Infield Fly Rule (until now), since that's the most famous badly-understood rule in baseball.
posted by cerebus19 at 1:11 PM on May 6, 2005

Probably because it has nothing to do with the question.

It's actually possible, though unlikely, for a pitcher to walk a batter he didn't pitch to

God, I love baseball.
posted by languagehat at 5:23 PM on May 6, 2005

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