Seen from both sides, "How much to hedge a bet?" leads to one event. Hedging and arbitrage both mean betting on more than one side of the same event. A hedge does it after a first bet is already placed, to lock in part of a win or cut a loss. Arbitrage does it at the start, across different books whose prices disagree, so that every outcome returns a little more than the total stake. What they share is the arithmetic of splitting stakes between opposite results.
Arbitrage betting meaning, in one line: backing every possible outcome of one event at different books, at prices high enough that the total return beats the total stake. How arbitrage betting works shows in the inverse sum: add up one divided by each best price, and a total below one means an opportunity exists. How to calculate arbitrage betting stakes: split the budget in proportion to those same inverse prices.
How to find arbitrage betting opportunities is mostly a matter of speed. Prices differ between books for minutes at a time, often after news, and the gap is usually one or two percent. Arbitrage betting risks are real despite the promise of a sure thing: a price can move before the second bet is placed, a bet can be voided for a palpable error, and settlement rules can differ between books.
How much to hedge a bet depends on the aim. To guarantee the same return on both sides, divide the first ticket's potential return by the decimal odds of the opposite side, and stake that. To only cover the first stake, bet less. Should I hedge my bet is a question about risk: every hedge pays the book's margin a second time, so a hedge bet strategy used on every ticket slowly costs money.
Yes. Each hedge pays the book's margin a second time, so a habit of hedging every ticket slowly eats into the overall return.
Two books can settle the same event differently, for example on retirements or overtime, which can leave one side of an arbitrage unpaid.
Yes. Accounts that only take arbitrage prices tend to be limited or closed, which ends most runs while the sums are still small.
Prices can move in the moments between two bets, and a changed price can turn a planned arbitrage into an ordinary bet with a loss.
A price the book considers obviously wrong can be voided under its terms, leaving the other half of the arbitrage standing alone.