Chelsea are odds-on favorites (at 10-11) to win the English Premier League. Next season. Man Utd are second favorites at 5-2, Arsenal close behind at 11-4. Every other club is a rank outsider - Liverpool is quoted at 14-1 and the rest are 66-1 bar. As Clive Tyldesley says in The Telegraph, "Unless Bill Gates takes an unexpected interest in Bolton Wanderers, the grid for the start of the next race will consist of four racing cars and 16 dodgems."
That's not a very balanced competition, in my view. Most measures of competitive balance are of an ex post nature - standard deviations of winning percentages, concentration of championships won, and so on.
Implicit in the betting odds are good approximations to the probabilities of winning a championship (unless you are a follower of Richard Thaler or even Steve Levitt). I've long thought that these ex ante measures offer a uniquely informative alternative to the traditional measures of balance in sports leagues.