What Is A Slugging Percentage In Baseball?

No bones about it – a batter’s slugging percentage is one of the most telling stats when it comes to judging how exciting his play is.

His slugging percentage is the number of hits that result in him being able to cover multiple bases, the moments in a game that really get the crowd out of their seats as the ball hurtles towards the edge of the field. These hits can be doubles, triples and home runs, each one indicating how many bases he can run after his shot.

Much like a shot in cricket that results in a batter scoring two, three, four or even six runs, the power with which the ball is hit is a big factor.

A player’s slugging percentage is determined by the number of bases they hit each time they are at bat. The stat is calculated by taking the total number of bases run and dividing by ‘at bats’. This produces a figure which is rounded off to three decimal places.

The figure assesses the number of bases a batter would be expected to cover every time he comes out to bat. So his skill in achieving hits which earn him extra bases, and the regularity with which he does this earn him a high slugging percentage.

The History Of The Slugging Percentage

In itself, it is a relatively new statistic, but various precursors have been used, all the way back to 1867, when The Ball Players’ Chronicle published an article by Henry Chadwick titled ‘The True Test of Batting’.

He advocated the use of a ‘total bases average’, using the total number of bases a player achieved in every game, and dividing it by games played.

The subtle change to using the number of bases while at bat, rather than per game, was adopted by the National League in 1923, and finally by the American League in 1946.

Chadwick believed that hits in isolation didn’t paint a true picture of a batter’s success, reinforcing his stance by saying that the SP did not take any account of on-field errors – which happened more often in that era, due to fielders not wearing gloves.

This is why it was not until 1952 that a slugging percentage stat first appeared on collectors’ cards, and it took right up to 1981 for it to be universally quoted.

How is a Baseball Slugging Percentage Worked Out?

This calculation uses two pieces of data, the number of times a player has been at bat, and the total number of bases he has covered.

The slugging percentage is the figure you get when you divide the player’s total number of bases by the number of times he has batted. The total base figure is value-added, that is, for each base more than one covered, you add one more to the total, so – second base, add one, third base, add two, home run, add three.

So written out, the formula is: 

1B + (2B x 2) + (3B x 3) + (HR x 4)/AB.

The batter’s slugging percentage only takes into account when he has been officially deemed to be at bat. That is, when he gets a hit, when he reaches first base as a result of a fielder’s choice, an error – usually by mishandling or a poor throw of the ball – or finally, if a put out is achieved against either the batter or a base runner.

So for example, if a batter has been at the plate 200 times, and in those has made 70 hits, of which 15 have been doubles, 10 triples, and five home runs, his slugging percentage is as follows:

40 (number of first-base hits) + (15 second base hits x 2) + (10 third base hits x 3) + (5 home runs x 4) = 120/200, or a slugging percentage of 0.600.

Complicating matters a little is the existence of a refined statistic related to slugging percentage, known as SLG-plus. This adjusts the batter’s slugging percentage to account for the dimensions of the ballparks and the league that the player was in. In addition, the number is ‘standardised’, so that the median is 100, with a score above 100 being better than average. The formula used to calculate SLG-plus is:

100*(SLG/lgSLG), where lgSLG is the league average for that year.

What Represents A Good Slugging Percentage?

It’s all well and good collecting players’ slugging percentages or rates, but coaches, players and fans all need to know what represents a benchmark over which a player is considered to be hitting above average.

As you can gather from the above details, it’s a little more complex than counting the number of goals scored by a soccer player, and is even more nuanced than the calculation used to work out a cricket batter’s average runs scored.

Slugging percentage can be affected by a whole variety of factors outside the batter’s control – anything ranging from the dimensions of the ball park, through the weather, to the number and variety of styles used by the pitchers faced. Historically, however, statisticians now believe that a good slugging percentage is upwards of 0.450, while if he managed to record a figure of 0.550 he would be considered outstanding. To illustrate, between 2005 and 2020, the top slugging percentage in the American and National Leagues was between 0.551 and 0.671. And eight players have had an average of above 0.650 in a season.

What Does A Player’s Slugging Percentage Tell Us About Him?

If we tell you that the player with the highest SP of all time is Babe Ruth (with a career average of 0.690), then you might guess that it just denotes someone renowned for big hitting.

The MLB’s official definition of Slugging Percentage tells us: “Although a double is not worth exactly twice as much as a single in the context of scoring runs, slugging percentage is still one of the best evaluators of power, because it accounts for more than just home runs.” So it’s a good measure of the way in which a player can evaluate the field, and place the ball in areas which allow him to score double and triple-base hits, as much as home runs.

In that respect, it is a far more reliable gauge of a batter’s skill.

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