Understanding Props Bets What They Are and How They Work

Come along for the ride as I show you all of the different props markets available, how to find inefficient lines at sports markets, and which scenarios are ideal for placing bets!

Props Betting Live & Direct

Before you even take a gander at the book’s line you need to handicap the market yourself. To come up with my own odds I pull the player's average in the stat category, weigh the last 10 games more heavily than the season average, and adjust for the opponent's defensive rating against that position.
You need to focus on home/away (teams score 5% more at home on average), pace of play, injury reports, and whether the game script favors high volume for that player ^[1].

The formula for a negative line is implied prob = |odds| ÷ (|odds| + 100). For a positive line: implied prob = 100 ÷ (odds + 100). I only pull the trigger if my true probability is at least 5 percentage points above the sportsbook's implied probability.

This is how my process looks in reality. Heading into Game 4 of the Knicks vs. 76ers second-round series, I put $100 on Jalen Brunson over 27.5 points at DraftKings at -106. My reasoning was the game is at Madison Square Garden, where Brunson historically elevates. 

Credit: DraftKings Sportsbook – Screenshot captured by Felix Dubler

Also, in the first three games of this series, he'd scored 35, 33, and 26, an average of 31.3 points, and Philadelphia still hasn't solved the Brunson pick-and-roll ^[2]. 

At -106, the implied probability is 51.5%. My model had him at ~62% to hit the over. That's a 10.5-point gap well above my 5% threshold. My $100 bet at -106 would payout $194.34 total if Brunson balls out.

How Books Create Prop Lines

Sportsbooks run quant models that ingest a player's season average, recent form, matchup data, usage rate, pace, and opponent defensive ratings. Once they land on a projected number, they set a line just above and below it and then add their vig to both sides.

Credit: DraftKings Sportsbook – Screenshot captured by Felix Dubler

Take Victor Wembanyama over/under 26.5 points as a live example. Wembanyama has averaged 25.0 this season and just dropped 39 points in Game 3 of the conference semis [4]. The sportsbook prices the market at:

• Over 26.5 at -114 - Implied probability: 114 ÷ (114 + 100) = 53.27%
• Under 26.5 at -112 - Implied probability: 112 ÷ (112 + 100) = 52.83%

You add those numbers up and you get 106.1%. The extra 6.1% slapped on is the sportsbook's vig. This is not too bad considering SGP bets typically feature 20% or higher vigs.

So as long as NBA and NFL betting environment roughly get the same action on the under/over, they’ll profit no matter how Wemby performs.

Props Betting Scenarios Worth Exploring

Props are predictable due to the abundance of sports stats available, however, based on my experience, sportsbooks are also very adept at setting lines. These are a few scenarios where you can still outsmart the betting apps.

In the NBA, when a star misses a game, usage redistributes. If Embiid sits, Maxey's assists and points lines should both shift up. Books often lag by half a game when injury news breaks during morning shootaround. I check injury reports at 11 am ET on game days, and props usually go live between 10 am and noon.

When a team's primary perimeter defender goes down, the opposing team's lead guard becomes a prime over candidate because the books are slow to adjust for. If the Sixers' best wing defender misses Game 4, Brunson's points line should be 2-3 points higher than it is. I strongly recommend betting early before the line corrects.

Rookie Prop Betting Moves

To avoid your bankroll going up in smokes, look out for these rookie errors that catch out a lot of prop bettors:

The average vig for prop bets is around 8%, which means you need to win 1% more of your wagers compared to spread bets to break even ^[3].

I track every prop bet with the odds I got vs. the closing line. If I'm consistently getting +CLV, my model is working; otherwise it calls for some tweaking. In the past I’ve even had to scrap entire models. 

I pulled up the First Points Scorer prop for Knicks vs. 76ers at DraftKings and calculated the implied probability for all 10 players. It added up to 118.3%, good luck beating an 18% vig over any decent sample size. If you must wager on first scorer markets, then pull up an MLS odds providers and stick to goal scorer bets, as the vig is much lower.

Also just because you love LeBron and want him to score 30+ points, don’t discount his current form and Father Time.