AFL line betting, explained
The line turns every game into a coin flip. When one side is $1.20 and the other $4.50, head-to-head is boring — so bookmakers offer a handicap that levels the contest: the favourite must win by more than a set margin, the underdog just has to keep it closer than that.
Reading the line
You'll see something like: Cats −24.5 ($1.90) / Kangaroos +24.5 ($1.90). The Cats "give" 24.5 points of start; the Roos "receive" it.
- Back Cats −24.5: you win if Geelong wins by 25 or more.
- Back Roos +24.5: you win if North wins, or loses by 24 or fewer.
Where the number comes from
The line is the market's expected margin. It's set so that, in the bookmaker's judgement, either side of the handicap is close to a 50/50 proposition — then priced at roughly $1.90 each way. Those prices imply 52.6% each (105% total): the ~5% overround is the fee, same as any market. If the money leans one way, books move the line (24.5 → 27.5) or shade the prices ($1.85/$1.95) until it balances.
How a model prices the line
A ratings model produces an expected margin — say Cats by 19 — and a spread of likely outcomes around it. AFL margins are noisy: historically the result lands about ±36 points (one standard deviation) around any expectation. Pricing "Cats −24.5" is then a maths question: what fraction of that outcome distribution has the Cats winning by 25+? If the model says Cats by 19, giving 24.5 start means covering less than half the time — the model would rate Roos +24.5 the value side even while expecting the Roos to lose the game. That's the line market's core trick: you're betting on the margin, not the result.
Line vs head-to-head: when each makes sense
| Situation | Better market |
|---|---|
| You think the favourite wins, but only just | Underdog on the line |
| You think the favourite smashes them | Favourite on the line (better than $1.15 h2h) |
| You think the underdog actually wins | Underdog head-to-head (the bigger payout) |
| Wet weather forecast | Lines compress — unders/underdog lean |
Traps to respect
- Garbage time cuts both ways. Junk-time goals decide line bets constantly. A 23-point margin becomes 29 in ninety seconds, and your +24.5 ticket dies after the siren's practically sounded.
- Don't double-count your opinion. "They'll win easily" is already priced into a 24.5-point line. The bet is only smart if you think the market's margin is wrong, not just that the favourite is good.
- The margin distribution is fat. ±36 points of noise means even a "certain" cover fails often. Size stakes accordingly — see betting responsibly.
Model-priced lines, every round
FootyAI converts model margins into cover probabilities and flags when either side of the line is priced wrong.
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