Over/Under (also called totals) is a market where you bet on whether the combined measurable output of a match — goals, points, runs — will exceed or fall short of a predetermined line. The result of the match itself is irrelevant; only the total matters.
In football, the most popular line is Over/Under 2.5 goals. Over 2.5 wins if there are 3 or more goals; Under 2.5 wins with 2 or fewer. Lines of 1.5, 2.5, 3.5, and 4.5 are all standard in football. Asian total markets add quarter lines (2.75, 3.25) for split-stake precision.
Research for totals focuses on teams' scoring and conceding rates, game style, match pace (expected goals models are particularly useful), venue, weather, and team selection. High-pressing, offensive teams tend to be involved in high-scoring games; defensive, counter-attacking sides tend towards lower totals. Head-to-head records between specific opponents also carry statistical relevance.
In-play totals betting is popular because the total shifts dramatically as goals are scored. Before a goal, the market sits at 2.5. After an early goal in a high-tempo match, the implied probability of more goals rises significantly. Experienced in-play bettors use pre-match research to identify when in-play totals prices are mispriced relative to the true probability.
Example
Manchester City host Brighton. Pre-match Over 2.5 Goals is priced at 1.60 (62.5% implied). You research City's average goals per game (2.8) and Brighton's tendency to concede in free-scoring matches. You back Over 2.5 at 1.60. City win 3-1. Total goals = 4. Over 2.5 wins. A £25 stake returns £40.