MLB advanced stats cheat sheet

If all the stats bandied about by writers and increasingly broadcasters have you confused, look no further!

Baseball, more than any sport, is a game of statistics. Sure, you can get wildly advanced statistics in any of the sports, but baseball is the one that did it first and the one that makes them the least coherent. In basketball, you want to track the number of points, rebounds, and steals. In football, it’s mostly just tackles and yards gained. But when it comes to baseball, nothing can be easy. Rather than track hits, one of the simplest and most commonly understood baseball stats, batting average, is the percentage of hits in a given number of at-bats - which are distinct from plate appearances.

For the purposes of this article, I’m going to assume that you know the stats that have long been a part of American sports vernacular such as batting average. Of course, if there are any stats not covered here, even the so-called simple ones, please ask about them in the comments below and I or one of the other amazing commenters will be sure to help you out. That said, it’s been a while since we had one of these on Royals Review and with the Royals holding a playoff spot as we approach mid-August it stands to reason that there are new baseball fans or lapsed baseball fans trying to come back who need a refresher course.

This is just going to be a quick break down for the need-to-knows of how to comprehend the numbers that will be flying at your head. If you want a deeper breakdown, including the formulas used, check out FanGraphs. Even I, a seasoned baseball writer and commentator, occasionally google something like “fangraphs FIP” in order to make sure I remember the formulas correctly.

And now, onto the cheat sheet

Some other stats that look like batting averages or ERAs

OBP - On-Base Percentage - the amount of times a runner reaches base (except for errors) divided by the number of plate appearances. A good rule of thumb is that anything over .350 is good, anything over .400 is fantastic.

SLG - Slugging percentage - the total bases (a single counts for one, double counts for two, triple for three, home run for four) divided by the number of at-bats. A good rule of thumb is anything over .400 is good, anything over .500 is fantastic.

OPS - On-base Plus Slugging Percentage - Exactly what it sounds like, this stat is often used as a shorthand for total offensive production because it accounts not just for the hits and not just for the times a player reaches base, but also for how often they hit extra-base hits.

BABIP - Batting Average on Balls in Play - The same thing as batting average or AVG, but ignores things like strikeouts and home runs. Is often used to indicate whether a player might be a little bit lucky. Usually .300 is about average. If someone has a .400 BABIP, their offensive numbers are probably inflated compared to what you can expect going forward. If they have a .200 BABIP their offensive numbers are probably deflated.

WHIP - Walks + Hits per Inning Pitched - What it says on the tins. It average the number of walks and hits allowed over the number of innings pitched. If you have a WHIP under one, you’re allowing fewer than one baserunner per inning and aren’t likely to give up many runs.

FIP - Fielding Independent Pitching - Since batted balls are often a bit lucky and whether they turn into hits can have a lot more to do with the fielders than the pitcher, this attempts to remove some of that luck from pitcher statistics. A good FIP is the same as a good ERA, anything lower than 4 is probably workable, anything lower than 3 is very good.

SIERA - Skill-Interactive Earned Run Average - Another stat that tries to take more into account that the simple number of earned runs allowed averaged over nine innings, with scales similar to ERA and FIP

Modern slash lines go AVG/OBP/SLG/OPS

Plus and minus stats

The first thing you need to know about + and - stats is that they are always pegged to 100 as an average, with + stats signaling that anything above 100 is that many percentage points better than average and - stats signaling that anything below 100 is that many percentage points better. These are usually aggregate stats, meaning they’re combining a lot of things to try and tell you some general information about a player.

One of my favorite of these is wRC+ which stands for Weighted Runs Created Plus. It’s a stat that has, as its average, the run creation environment in a given year. So, for example, you might want to compare the OPS of two players to gauge their total offensive output. But that doesn’t work across eras because the run-scoring environments can be drastically different. You can compare wRC+ stats to see if they were similarly better than the other hitters in that season because it’s just a percentage difference from the league average. Even when you’re not performing comparisons, however, it’s useful because if you know that Bobby Witt Jr. has a 171 wRC+ you know he’s 71% better at creating runs for his team than a league average player in 2024. And that’s a lot!

wRC+ - how good a hitter is, higher is better, 100 is league average

OPS+ - how good a hitter is, higher is better, 100 is league average

ERA+ - how good a pitcher is, higher is better, 100 is league average

ERA- - how good a pitcher is, lower is better, 100 is league average, calculated differently from ERA+

The /9 stats

When talking about pitchers you’ll often see stats like H/9, BB/9, K/9, or HR/9. These take the hits, walks, strikeouts, and home runs a pitcher allows and divides the number by 9 to give a rate stat that allows pitchers to be compared with each other even when they’ve pitched different numbers of innings. This is especially useful in the modern game where one-inning relievers are more prominent than ever. If you want to know if someone is good at striking out batters, the raw number of strikeouts may not tell you much, but if he has a high K/9 then you know that he does, indeed, strike a lot of batters out even if he hasn’t pitched many innings.

Some good numbers to look for:

K/9 - Anything over 10.00 is considered pretty good. Anything less than 9.00 in the modern era can signal an inability to finish hitters off

BB/9 - Anything over 3.50 is a lot, if it’s under 2.00 they’re very good.

HR/9 - This is a number you usually want to see under 1.00. If it’s much over 1.00, it’s pretty scary.

Another stat to keep an eye on here is the relationship between the K/9 and the BB/9. If the pitcher’s K/9 is three times more than the BB/9, then they’re probably doing really well even if they have a high BB/9 or a low K/9. This is because they’re showing an ability to avoid free baserunners or they’re keeping hitters from even getting the ball in play so the walked batters are stranded.

Sometimes you will also see people use K% or BB% instead of K/9 and BB/9. The idea is the same, it’s just that instead of showing the stat in relation to the innings pitched, it shows it in relation to the number of batters faced.

K% - Average is usually around 20%, lower than 15% is bad, higher than 25% is elite.

BB% - Average is usually around 8%, higher than 9% is bad, lower than 7.5% is very good

K-BB% - Literally just subtracting the BB% from the K%, average is about 14, higher than 20 is very good, lower than 10% is pretty bad

That should about cover the majority of the stats you’re likely to run into. Again, if there is anything I missed or anything you don’t understand, feel free to ask in the comments below and I’ll do my best to answer. Remember, you’re not dumb if you don’t understand this stuff, you just haven’t had a chance to learn it, yet.

WAR

I just realized I completely forgot to write about WAR, so I am adding this after publication.

Wins Above Replacement, or WAR, is an aggregate stat that tries to take a holistic approach to measuring a player’s contributions to their team in terms of how many more win above a random AAA guy they are contributing to the team. Baseball rReference and FanGraphs each have their own versions (called bWAR and fWAR respectively,) that use slightly different calculation and different people will prefer different versions. Generally speaking, however, 2 WAR for a full season is considered “starting player” good, 4-5 WAR is considered All-Star level while, 6 WAR or more should put you in the MVP conversation. There have only been a little more than 50 player seasons where a player managed to accrue 10 WAR or more. It’s incredibly difficult and special.

It is possible to have a negative WAR, which would mean you are actively hurting your team as compared to what would be expected from promoting any random guy from AAA to fill that position.

Based on those descriptions, it will not surprise you to discover that Adam Frazier has a 0.2 bWAR and a -0.7 fWAR while Bobby Witt Jr. has already accrued a 7.6 bWAR and a 8.0 fWAR, and is still on pace to finish with something between 10 and 11 fWAR at last check. If you’ve thought to yourself, “How many fewer games would the Royals have won without Bobby Witt Jr.?” the answer is approximately eight with more than a quarter of the season remaining. That’s a very good player, indeed.