In a single-leg knockout match, one game determines who advances. There are no second chances, no aggregate scores to overturn. Win and you progress; draw and you play extra time and possibly a penalty shootout; lose and you are out. This format is used in domestic cups (the FA Cup, the Copa del Rey), the latter stages of major tournaments (World Cup knockouts), and some early rounds of European competition.
A single-leg knockout fundamentally changes how teams approach a match compared to a league fixture. Key differences:
The FA Cup uses single-leg knockouts with replays for drawn matches (though the replay system has been phased out in recent rounds). This means giant-killings — lower league clubs defeating top flight teams — are a structural feature of the competition. The combination of one-game knockout format, venue advantage for lower-league home sides, and squad rotation by Premier League teams creates conditions where an upset every round is statistically expected.
When a single-leg knockout ends level after 90 minutes, most competitions proceed to 30 minutes of extra time (two 15-minute halves) and, if still level, a penalty shootout. Penalties are a lottery of skill and nerve that introduces a significant random element — strong teams lose cup ties on penalties regularly. The statistical evidence suggests that penalty outcomes are only weakly predictable, making "cup runs ended on penalties" as much a feature as an anomaly.
