Hit rates and sample size: what 7 out of 10 really means

A hit rate is the share of games a player went over a line: 7/10 means he cleared it in 7 of his last 10. It is the most popular number in prop betting, and the most misread.

Luck hides in small samples

Take a bet that is truly 50/50, a coin flip. Over 10 games, how often does it come up over at least 7 times? About 17% of the time. One in six coin flips looks like a "70% bet" over ten games.

Over 20 games the noise is still large: a true 50% bet will show anywhere from about 30% to 70% most of the time. Ten games is a story, not proof.

Read the windows together

NBA House shows the last 5, 10 and 20 games and the season. Read them as a set:

• All windows agree (L5, L10, L20 and season all high): the line is probably too low, unless something changed.
• Short window high, long window average: a hot streak. Ask why: more minutes, a teammate out, a new role? If there's no reason, expect it to cool.
• Short window low, long window high: a slump, or a real change. Again, look for the reason.

The line moves too

A hit rate counts tonight's line against old games. If the line was 21.5 a month ago and is 25.5 tonight, his old games weren't played against this number. Check whether the line has caught up with his form.

What really matters

Hit rates describe the past. What predicts the future is the reason behind the numbers:

• Minutes: is he playing more, or less, than in those games?
• Role: usage, shots, who is out tonight.
• Matchup: the opponent's defense against his position, and the pace.

Use hit rates to find questions, then answer them with minutes and role. The with/without filter on NBA House shows how a player's numbers change when a teammate sits.