After Nelson Cruz’s dramatic walk-off grand slam on Monday, there’s been a lot of talk about whether or not it was really the first walk-off slam in postseason history. You see, Robin Ventura also hit a home run with the bases loaded to end Game 5 of the 1999 NLCS, in the 15th inning no less. However, he was never credited with a home run because as he rounded first base, teammate Todd Pratt (who had been on first base) turned around and hugged Ventura. As the rest of his Mets teammates poured onto the field, it became clear that Ventura would not finish rounding the bases.

Officially, he was only credited with an RBI single, leading to the play being called a “grand slam single.” Luckily, Ventura’s hit still won the game, albeit by a score of 4-3 rather than 7-3. For some other ill-fated hitters, a rain delay, bad call or even a paper airplane led to home runs being called back, sometimes with serious consequences.

In fact, two other grand slams have been downgraded to singles, both because of a rule that forbids runners to pass any teammate ahead of them on the base path. Both hits – one in 1970 by Dalton Jones of the Tigers, the other in 1976 by Tim McCarver of the Phillies – went over the fence, but saw the hitter run past the runner that had been on first base. Only the hitter was called out, so in both plays they got three RBIs and were credited with a single, but no grand slam.

In 1965, a lost home run gave us one of Yogi Berra’s greatest quips. The Mets were playing in Cincinnati, where construction near Crosley Field meant that the outfield wall was concrete, but topped with plywood in an attempt to keep balls in the park. According to officials, the concrete was in play, but any ball that hit the plywood would be a home run. With the bases loaded, outfielder Ron Swoboda hit a ball that bounced off the plywood and back onto the field, where the umpires erroneously ruled it in play. Coach Yogi Berra was ejected for protesting the call and later told reporters "Anyone who can’t hear the difference between wood and concrete must be blind."

In 1929, Tigers third baseman Frank Sigafoos hit his first ever home run in a road game against St. Louis. However, the umpire had actually called a balk on the pitcher and declared a dead ball, thus nullifying the home run. It would turn out to be the only time Sigafoos would ever hit the ball out of the park, and he finished his career with no official home runs.

In 1978, a paper airplane of all things erased a John Lowenstein home run. A fan threw a paper airplane onto the field just as Angels pitcher Paul Hartzell was winding up. The umpire called time because of the interference, but Hartzell finished pitching and Lowenstein ended up taking the ball over the right field fence. However, the hit was called back because of the time out. Lowenstein would eventually walk and ended up scoring in the inning.

St. Louis outfielder Joe Medwick ended the 1937 season tied with Mel Ott for the National League lead in home runs with 31, although he still won the batting triple crown thanks to a dominating season. However, were it not for one rained out game, he would have secured the outright home run lead. In a double-header against the Philadelphia Phillies, Medwick hit one out in the first inning en route to a 10-2 Cardinals lead. Thanks to an earlier rain delay, it was getting dark and officials were worried the stadium would have to close. The Phillies started slowing the game down by taking repeated trips to the mound and requesting ball changes in a bid to force the teams off the field before the game became official in the fifth inning. The tactics worked and the umpires called the game off in the fourth inning, erasing all of the official stats and the home run that Medwick could have used to break his tie with Ott.

Interestingly, a rain-out also erased a Stan Musial home run in 1948, which ended up eliminating his chance to become the first NL triple crown winner since Medwick.

For more lost home runs, check out this exhaustive list from Retrosheet.org. And for a good laugh, check out this Onion article about Hank Aaron’s 50 lost home runs, conveniently restored as Barry Bonds was nearing the home run record.