If two runs have already been completed and the striker is then run out while attempting a third, the batting side keeps the two completed runs. The third run is not added because it was still in progress when the wicket was put down. This is the ordinary case, without a runner or penalty runs.
How the third-attempt run is counted
Hypothetical example: The batters complete the first run and both reach their opposite creases. They turn again, complete the second run, and begin a third attempt. Before the striker reaches the far crease, a fielder fairly breaks the wicket at that end while the striker is out of the ground. The result is a run-out dismissal and two completed runs for the batting side—not three. Under MCC Law 38 on run out, completed runs before the wicket is put down stand, while the run in progress does not count, subject to the law’s stated runner exception.
This example assumes the run-out is valid and the two earlier runs were completed correctly. Its narrow question is the score after that decision, not whether a particular camera frame proves the dismissal.
Contrast: wicket broken before the first run
Counterexample: The striker hits the ball, leaves the crease, and the batters set off. Before either run is completed, a fielder breaks the relevant wicket while the striker is out of the ground. In that situation, no completed run exists before the dismissal, so the result is zero runs from the running attempt. The completed-run count changes the outcome.
Limits of this ordinary case
These examples exclude a runner, penalty runs and other special circumstances. They address only completed running, not bowler credit or match predictions. For a real incident, confirm the official decision and applicable playing conditions before reconciling the score.