The hold, also called 'vig' or 'juice' is the margin (percentage of every dollar wagered) built into both sides of a wager that the sportsbook keeps for themselves.
Different bet types will carry different margin amounts. Obviously, higher percentages are less desirable for most customers.
Ideally, sportsbooks would simply have the same amount of money on both sides of a bet and just collect the hold but that isn't always the case.
Implied probability plays into understanding the hold concept. Understanding that when looking at probabilities in sports betting, the number is going to be greater than 100%. To see this, you need to convert the odds of both sides of a bet into probabilities and add them together. Subtract 100 from that number and you are left with the hold the book charges on that bet.
Typically, holds are less than 5% for a two outcome wager like an NBA moneyline. ?When there are wagers with more outcomes the hold percentage is higher.
Calculating the hold is also important when considering the projections of the likelihood that the event you are betting will happen. Removing the hold will make that comparison clearer.
To do that, you divide the first team's implied probability by the sum of all probabilities.
For example, the line on the Celtics is +150 and the sportsbook is showing the Lakers as -175. The implied probability is 40% for the Celtics and 63.65% for the Lakers. The sum of those probabilities is 103.65%. So to find the true probability of the Celtis to win, you would divide 40 by 103.65 and get the result of 38.6.