I want to back underdogs in LoL but only when the odds are really off
Then the entry should compare the market to the draft, not to the standings.
Buy the underdog when it is priced under 30¢ and has the stronger late-game composition. Hold through the mid game, and sell if the price reaches 50¢.
how often does that happen?
Rarely: about one match in nine over the past month. The agent would be idle most days, which is the point of a rule this strict.