Definition
A z-score tells you how far a number is from the average, measured in standard deviations. In betting, it can show whether a team stat, player prop projection, or market price is unusually high or low compared with its normal range.
Formula:
z = (value - mean) / standard deviation
A z-score of 0 means the value equals the average. A z-score of +2 means it is two standard deviations above the average. A z-score of -1 means it is one standard deviation below the average.
Worked Example
A player’s rushing yards average is 60, with a standard deviation of 12 yards. A sportsbook posts his rushing prop at 78.5 yards.
Using the formula:
z = (78.5 - 60) / 12
z = 18.5 / 12 = 1.54
The prop line is 1.54 standard deviations above the player’s average. If the over is priced at -110, a bettor risks $110 to win $100, but the z-score only describes how stretched the line is compared with the player’s past distribution. It does not calculate payout or win probability by itself.
Why It Matters
Z-scores help bettors compare stats on the same scale, even when the raw numbers are different. They are useful for spotting outlier lines, checking projections, and deciding which props deserve deeper review.