you see, what determines the spread is the activity of gamblers, not so much the bookies. when the bookies see that their book is getting lopsided they change the spread to encourage more betting on the other side. an absolutely balanced book means the bookies simply transfer money from losers to winners - making their cut on transaction fees, low risk and really rather mechanical. the bookies, instead of exerting a house advantage (see, eponymous book by jeff ma in my brane fud section), function more like market makers, simply facilitating wagers for a fee.
one can check the spread online because sports gambling is legal in certain states and countries. as of 11am today the spread on tonight's broncos vs. seahawks game was 2.5 points in favor of the broncos, meaning, the broncos must win by 2.5 points to beat the spread. this is pretty narrow, less than a field goal, so tonights game is viewed by gamblers as being fairly evenly matched.
there is something very much akin to a betting spread in the options market that comes into play during market events. in the world of options the events that generate interest like this are earnings reports. now, one might think that the analyst expectations for earnings of a company would be a kind of spread but these really reflect the opinion of a small number of people who may or may not be biased by who is or is not paying them. instead, the spread on a company's earnings report can be determined by an option strategy called a straddle.
buying a straddle means purchasing a call and a put at the same strike and same expiration. usually the strike chosen is an at-the-money strike. here is what the risk profile of a straddle looks like for kors (last: 79.93), which reports earnings tuesday morning:
|kors straddle expiring in 6 days|
personally, i hardly ever initiate a transaction to buy a straddle because it is at best a 50/50 proposition. market makers recognize that particpants overpay for options near earnings reports and they actually have a rule of thumb that says that the expected move in the market is really about 85% of this straddle price or $6.38. so the better bet is to sell this straddle but that has unlimited upside risk and nearly unlimited (bounded by zero) on the downside. this 6.38 market-maker expected-move is important to us premium seller's when we construct trades to take advantage of the volatility crush after earnings. (see tastytrade's trade-small-trade-often segment for examples of such trades.)
good luck on the super bowl tonight and may the odds ever be in your favor!