Move the players yourself — the offside rule explains itself in 30 seconds.
📖 One sentence: at the moment of the pass, if the receiver is in the opponent's half and closer to the goal than both the ball and the second-last defender (the yellow dashed line), it's offside. In short: no waiting by the goal!
Drag blue #9 (you) and the red defenders — the yellow dashed offside line follows them
Blue just passed to #9. You are the referee — what's the call?
How to use
Start in "Try it yourself": drag the blue attacker and the red defenders, press Pass, and watch the call change. The yellow dashed line always marks the second-last defender — that is the offside line. When it clicks, switch to Referee mode and judge 10 passes yourself. Wrong answers are free: every call comes with an explanation of why.
The rule stated precisely
A player is in an offside position if they are nearer to the opponents' goal line than both the ball and the second-last opponent, in the opponents' half. Being in that position is not an offence by itself. It becomes an offence only when a teammate plays the ball and the player is then involved — by touching it, by interfering with an opponent, or by gaining an advantage from where they were.
The second-last opponent is usually the last outfield defender, because the goalkeeper is normally the last of all — but not always, and the rule deliberately says second-last rather than last defender so that a goalkeeper who has come forward does not change the meaning.
Timing is what most people get wrong. The position is judged at the moment the ball is played by the teammate, not when it is received. A player can be well past the defence when the ball arrives and still be perfectly onside if they were level at the moment of the pass.
When there is no offside at all
In your own half. A player level with or behind the halfway line can never be offside.
From a throw-in, a corner kick or a goal kick. All three are explicit exceptions in the laws.
When level with the second-last opponent. Level is onside, which is why the tightest calls come down to a shoulder or a foot.
When the ball is played backwards. If the ball comes from nearer the opponents' goal than you are, you cannot be offside from it.
When an opponent deliberately plays the ball to you. A defender's own clearance or pass resets the situation.
Why the rule exists
Without offside, the most effective tactic in football would be to leave a player permanently next to the opponents' goal and pass to them over the top. Games would become long kicks between two crowded penalty areas, and the midfield would empty out. The rule forces attackers to stay behind the ball until it is played, which is what keeps the teams compressed and the play connected.
It also created the defensive tactic that makes the rule visible. A back line that steps forward together the instant before a pass leaves an attacker stranded ahead of it — the offside trap, a coordinated move that turns a rule about attackers into a weapon for defenders.
At the exact moment a teammate passes the ball, the receiver must not be closer to the opponent's goal than both the ball and the second-last defender (usually one outfield defender, since the goalkeeper is the last). If they are, the referee calls offside. The rule exists to stop attackers from simply camping next to the goal.
When is it NOT offside?
You can never be offside in your own half, when you are behind the ball at the moment of the pass, or when at least two opponents are between you and the goal. Real matches also exempt throw-ins, goal kicks and corner kicks — this trainer focuses on the main pass situation first.
Is this suitable for kids?
Yes — it was designed for complete beginners including children. There is no reading-heavy rulebook, no time pressure, no penalties for wrong answers, and no chat or user content. Just drag, pass and learn.
Does the trainer cover VAR and edge cases?
Not yet — on purpose. Professional edge cases (deliberate play by a defender, interfering without touching the ball, VAR line calibration) confuse beginners before the core idea has settled. Master the yellow line first; the fine print will make sense afterwards.
Is it offside if the attacker is exactly level with the second-last defender?
No — level is onside. Offside requires the attacker to be clearly nearer to the goal line than both the ball and the second-last defender; when it's too close to call, the benefit of the doubt goes to the attacker. Also, only body parts that can legally play the ball count — hands and arms are ignored when drawing the line.
Is standing in an offside position by itself a foul?
No. Being in an offside position only becomes an offence when the player gets involved in active play — receiving the pass, challenging an opponent for the ball, or blocking the goalkeeper's view. An attacker can stand beyond the line without consequence; the flag is raised only when the ball is played toward them and they take part.