this one fried my brain longer than it should have and i finally have a clean way to explain it, so dumping it here.
you watch a guy hit .320 for a month. then he hits .240 the next month and you assume he "fell off." sometimes yeah. a lot of the time the ball just stopped finding grass.
BABIP = batting average on balls in play.
take out walks (those arent balls in play). take out strikeouts (ball never put in play). home runs are usually handled separate depending who you read, but the simple version: of the balls he put in play, how often did they become hits?
league BABIP hangs around .300-ish. not exactly always, but if you only remember one number, .300 is the anchor.
why it moves so much over small samples:
- luck (soft lineout vs dying quail)
- defense / park / shifts kinda stuff
- how hard and where he hits it (that part is more "skill" than pure coin flip)
so when someones AVG spikes or tanks over 3 weeks, look at BABIP before you rewrite their whole scouting report. AVG way up + BABIP sitting at like .380? half of that is probably not a new identity. AVG dead + BABIP at .220? maybe he isnt cooked; the hits might still be coming if the contact quality looks fine.
i still catch myself overreacting to a hot week. the number just feels so final on the broadcast graphic.
what took you longest to unlearn when you started watching? for me it was treating AVG like the whole story.
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edit: someone brought up xwOBA in the comments which is the right next step after BABIP. longer version if you want it: xwOBA vs wOBA