One run shall be scored each time a runner legally advances to and touches first, second, third and home base before three men are put out to end the inning. EXCEPTION: A run is not scored if the runner advances to home base during a play in which the third out is made (1) by the batter-runner before he touches first base; (2) by any runner being forced out; or (3) by a preceding runner who is declared out because he failed to touch one of the bases.
Example 2 (Video): During the 6/1/12 Orioles-Rays game, with one out and the bases loaded, B1 hit a fly ball to center fielder F8 who threw into second base as all runners tagged. Prior to the runner from third, R3, touching home plate, the runner from first, R1, was retired at second base. No run.
Example 3 (Video): During the 6/29/12 Mets-Dodgers game, with runners on first and third base (R1, R3)—and assuming one out as the video description incorrectly indicates—B1 hits a fly ball to F8, who catches it on the fly as R1 and R3 tag. As R3 runs home, the third baseman F5 cuts off F8's throw, firing to the second baseman F4, who tags R1 for an [inning-ending] double play barely after R3 touched home plate. Run scores.
Example 4 (Video): During the 5/9/12 Giants-Dodgers game, with two outs and runners on first and second base, B1 hits a sinking fly ball to F8, who fields the ball on a bounce and throws behind R1, who had rounded second base. Replays indicated F4 applied the tag on R1 prior to R2 touching home plate. No run.