Hey Barry, I'm looking at the first tryscorer market where you get your money back if a player scores. Say Radradra, at $9. How would you go about working out whether this is a profitable bet? Or how profitable? I'm thinking he scores about once every two games (given doubles and triples), but how likely he is to score first is a mystery.
Well, that's a tricky one even if we assume that players have the same average strike rate across the season, regardless of opposition / conditions etc. There's no useful magic formula, but a basic approach might include (this is a gross simplification....and I'm doing it off the top of my head so I might f**k something up:
If the bet is for Parra 1st try scorer:
How often does Semi score (50% of games, say)?
Pretend the rest of the team selected are one player (with a really big name like RobinsonHoppaTakaMorgsCoreySandow.......). How often do they collectively score (say 4 times per game = 400% of games).
Then I'd probably say well, there a 50% chance of Semi scoring at all, so he score half a try a game. However, with the rest of our team scoring on average 4 tries per game, and assuming the order of tries scored is random I'd say Semi is a 0.5 / 4.5 = 1/9th chance of being our first try scorer.
If the bet is First Try Scorer in the Match (for either team), then you'd have to also consider how many tries the opposition score on average. If the opposition score 6 per game on average then Semi's chances of being first are 0.5 / (4.5 + 6) = approx 1/20. So you'd need a price of $21.00 for it to be a fair bet.
All of this assumes that there's nothing that systematically causes some players to score earlier in games, and other to score later etc.
If you can be bothered, you can work out how much the entire market is set against you.
If you take the dividend offered for each player, and divide 1 by this dividend
Eg. if Semi is $9 , 1/ 9 = 11.11%, Joe blogs is $15, 1/ 15 = 6.66% etc
Do it for every player. Add up the percentages. If the market is a perfectly fair bet (it wont be) they will add up to 100%. The greater the difference between the actual percentage and 100% the bigger the bookies margin. Starting price at the races might be as good as 105%. The take on exotic bets is often well in excess of 15% and much more where fixed prices are offered.
* if you are quoted odds rather than dividends 1 / (Odds +1)
Again, this ignores a number of complications.