The biggest difference is that rugby is more continuous, while football (usually meaning American football) is more stop-and-start with set plays and downs. In rugby, tackles do not end the play, and the ball must usually be released so others can contest it; in American football, the play stops when the ball carrier is downed.

Quick Scoop

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Feature Rugby American football
Ball movement Passes must go backward; players usually advance by running or kicking.One forward pass is allowed per play, from behind the line of scrimmage.
After a tackle Play continues, and the ball can be contested.Play stops, then teams reset for the next down.
How scoring works A try is scored by grounding the ball in the in-goal area; kicks can also add points.A touchdown scores 6 points, with extra-point options and field goals.
Game structure Usually 80 minutes total, often 15 players per side in rugby union.Four quarters, 11 players per side.
Substitutions More limited, so players often play both offense and defense.Frequent substitutions are normal, with separate offensive and defensive units.

In plain English

Rugby feels more like one long flow of possession, where players keep moving, tackling, and recycling the ball. Football feels more like a series of short tactical bursts, where each snap is a separate play.

Easy way to remember it

If you see frequent pauses, huddles, and planned plays, you’re probably watching American football. If the game keeps moving after contact and players fight to keep possession alive, you’re probably watching rugby.