Middle (middling)
Betting both sides of a spread or total at different lines so that a result landing between them wins both bets, while any other result loses only the vig.
If one book has the Padres −1.5 and another has the Twins +2.5, a two-run Padres win cashes both tickets. Middles are not arbitrage: most of the time one bet wins and one loses, costing the vig, and the profit comes from the occasional result inside the gap. Whether that trade is positive expected value depends on how often the middle hits.
ArbMonster separates the two: it reports true arbitrage (same line, prices summing under 100%) as opportunities and does not count line disagreements as edges.
Related terms: Point spread · Total · Arbitrage