Slugging Percentage
Bases per at bat: a single is 1, a double 2, a triple 3, a homer 4.
What it actually is. Total bases per at bat: one for a single, two for a double, three for a triple, four for a home run. It measures how far a hitter moves the line, not how often.
What a scout reads off it. Slugging is the damage half of a hitter. Read it next to average and the difference between the two, isolated power, is the part that is really about the bat rather than the base hits.
Where the lines are. The ceiling of the scale is 4.000 and nobody lives near it. .500 is a genuine slugger, .400 is respectable, .350 is a hitter getting by on singles. Babe Ruth's career mark of .690 has stood as the record since he retired in 1935.
How it lies to you. It is per at bat rather than per plate appearance, so a hitter who walks a lot is rewarded, and it insists a double is worth exactly two singles, which no run-scoring model actually believes. That mismatch is why weighted on-base average exists.
Batter's Eye: look up anything in baseball