On-base Plus Slugging
On-base plus slugging: getting on and doing damage, in one number.
What it actually is. On-base percentage and slugging added together. Two numbers with different denominators stacked on top of each other, which is mathematically improper and works anyway.
What a scout reads off it. It is the fastest honest read on a hitter in the game. One number, no lookup table, and it lands within a hair of far more careful measures for almost every player. When a broadcaster wants to say a hitter was good in one number, this is the one.
Where the lines are. .900 is an All-Star, .800 is solidly above average, .700 is a bottom of the order bat, 1.000 is an MVP season. Those four landmarks cover almost everyone you will ever look up.
How it lies to you. It undervalues on-base percentage, which is worth roughly one and a half times slugging in actual runs, so it slightly flatters sluggers who do not walk. It also ignores park and era completely, which is what OPS+ is for.
Batter's Eye: look up anything in baseball